Missed Warnings: The Fatal Flaws Which Doomed Challenger 32 Years Ago (Part 2)

This photograph of the space shuttle Challenger accident Jan. 28, 1986 was taken by a 70mm tracking camera at UCS 15 south of Pad 39B, at 11:39:19.261 EST. Photo credit: NASA

At 11:39 a.m. EST on 28 January 1986, the unthinkable happened, when shuttle Challenger was lost, a mere 73 seconds after liftoff. All seven astronauts of Mission 51L, including schoolteacher Christa McAuliffe, were killed in the tragedy.

Yet, as outlined in yesterday’s “PART 1” commemorative AmericaSpace feature, the human tragedy was accompanied by another: for it was equally tragic that the catalog of calamities which befell the shuttle program in its early years and eventually brought down Challenger could have been avoided. Warning signs had been thrown up repeatedly by previous missions, but were either dismissed or not treated with timely seriousness. In this second article, AmericaSpace looks back at the fateful decisions made on the eve of Challenger’s final flight and the incessant schedule pressures and “Go-fever” which eventually destroyed a flawed belief in the shuttle’s invincibility.

In late April 1985, three months after the Solid Rocket Boosters (SRBs) of Mission 51C had first drawn the attention of Morton Thiokol structural engineer Roger Boisjoly, another shuttle crew took flight. Mission 51B carried the Spacelab-3 payload, and subsequent examination of its boosters indicated erosion of the secondary O-ring, pointing clearly to a failure of its primary counterpart. As noted in yesterday’s history article, it was the latest in a worrying string of events which highlighted the failings of the shuttle vehicle and the management decisions which would doom Challenger on Mission 51L on 28 January 1986.

Challenger roars into orbit on 29 April 1985, mission STS-51B. Photo Credit: NASA

The 51B problem was attributed to leak check procedures. So serious was the episode, however, that “a launch constraint was placed on flight 51F and on subsequent launches,” read the Rogers Commission’s report into the Challenger accident. “These constraints had been imposed, and regularly waived, by the Solid Rocket Booster Project Manager at Marshall [Space Flight Center in Huntsville, Ala.], Lawrence B. Mulloy. Neither the launch constraint, the reason for it, or the six consecutive waivers prior to 51L were known to [NASA Associate Administrator for Space Flight, Jesse] Moore or [Launch Director Gene] Thomas at the time of the Flight Readiness Review process for 51L …

In fact, as Mission 51B’s commander, Bob Overmyer, would later discover, his own launch had been milliseconds from disaster. Crewmate Don Lind journeyed to Thiokol in Brigham City, Utah, for further explanation. “The first seal on our flight had been totally destroyed,” recalled Lind in his NASA oral history, “and the [other] seal had 24 percent of its diameter burned away. Sixty-one millimeters had been burned away. All of that destruction happened in 600 milliseconds and what was left of that last O-ring, if it had not sealed the crack and stopped that outflow of gases—if it had not done that in the next 200 to 300 milliseconds—it would have gone. You’d never have stopped it and we’d have exploded. That was thought provoking! We thought that was significant in our family. I painted a picture of our liftoff, then two great celestial hands supporting the shuttle, and the title of that picture is Three-Tenths of a Second. Each of [my] children have a copy of that painting, because we wanted the grandchildren to know that we think the Lord really protected Grandpa.”

Shortly after the analysis of the 51B boosters, on 31 July 1985, Roger Boisjoly expressed his growing concerns over the O-ring joint seals in a memorandum to Thiokol’s vice president of engineering, Bob Lund. “The mistakenly accepted position on the joint problem,” he wrote, “was to fly without fear of failure and to run a series of design evaluations which would ultimately lead to a solution or at least a significant reduction of the erosion problem. This position is now changed as a result of the [51B] nozzle joint erosion, which eroded a secondary O-ring with the primary O-ring never sealing. If the same scenario should occur in a field joint—and it could—then it is a jump ball whether as to the success or failure of the joint, because the secondary O-ring…may not be capable of pressurization. The result would be a catastrophe of the highest order: loss of human life.”

Close-up view of the rubberized O-ring seals within the Solid Rocket Booster casing. These seals were intended to prevent a leakage of hot gases, but on Mission 51L they failed spectacularly. Photo Credit: NASA

Boisjoly recommended the establishment of a Thiokol team to investigate and resolve the problem, and, on 20 August 1985, Lund duly announced the formation of a task force. However, only a day earlier, in a joint Thiokol-Marshall briefing to NASA Headquarters in Washington, D.C., on the issue, program managers concluded that the O-rings were a “critical” issue, but that, so long as all joints were leak checked with a 200 psi stabilization pressure, were free of contamination in the seals, and met O-ring “squeeze” requirements, it was safe to continue flying.

As the year wore on, Thiokol’s O-ring team, which had only 8-10 members, found many of their efforts frustrated by senior management. “Even NASA perceives that the team is being blocked in its engineering efforts to accomplish its task,” Boisjoly wrote in a 4 October memo. “NASA is sending an engineering representative to stay with us, starting 14 October. We feel that this is the direct result of their feeling that we [Thiokol] are not responding quickly enough on the seal problem.”

A little over three weeks later, on 30 October 1985, Challenger flew Mission 61A, experiencing nozzle O-ring erosion and blow-by at the SRB field joints; neither of these problems were identified at the Flight Readiness Review for the next mission, 61B, in November. Indeed, that flight also suffered nozzle O-ring erosion and blow-by. By early December, in response to these problems, Thiokol recommended that their testing equipment needed to be redesigned.

Only days later, on the 10th, the company requested closure of the O-ring critical problem issue, citing satisfactory test results, future plans, and work carried out thus far by its task force. This closure request was harshly criticized by the Rogers investigators. One panel member pointed out to the Thiokol senior managers: “You close out items that you’ve been reviewing flight by flight—that have obviously critical implications—on the basis that, after you close it out, you’re going to continue to try to fix it. What you’re really saying is [that] you’re closing it out because you don’t want to be bothered.”

Challenger roars into orbit on the morning of 5 October 1984. Photo Credit: NASA

Part of the problem was NASA’s desire, since the mid-1970s, to create a reusable transportation system that would provide regular and routine access to low-Earth orbit. Original plans to fly the shuttle once every fortnight, admittedly, were unrealistic with only four operational orbiters—rather than six or seven—but in its December 1985 launch schedule, the agency envisaged staging up to 24 missions per year from 1987 onward.

In correspondence with this author, one former shuttle engineer expressed serious doubts that such flight rates were achievable, even with overtime and three shifts working around-the-clock in the Orbiter Processing Facility (OPF). Nine or 10 missions in any 12-month period stretched resources to their limits. Overtime and overwork presented their own problems. Numerous contract employees at the Kennedy Space Center (KSC), the Rogers Commission heard, worked 72-hour weeks and frequently supported 12-hour shifts. “The potential implications of such overtime for safety were made apparent during the attempted launch of Mission 61C on 6 January 1986,” read the report, “when fatigue and shift work were cited as major contributing factors to a serious incident involving a liquid oxygen depletion that occurred less than five minutes before scheduled liftoff.”

Furthermore, the commission discovered disturbing evidence that NASA’s provisions to support the projected 24-flight annual rate were woefully inadequate. Spares for individual orbiters were in short supply (only 65 percent of the required parts inventory was in place by January 1986), leading to an increasingly dangerous practice of “cannibalism” from one vehicle to equip the next, and resources focused primarily on “near-term” problems, rather than longer-term issues. An $83.3 million budget cut in October 1985 necessitated additional major deferrals of spare parts purchases. The cannibalism of parts, said STS-6 veteran Paul Weitz, then deputy chief of the astronaut office, in his Rogers testimony, “increases the exposure of both orbiters to intrusion by people. Every time you get people inside and around the orbiter, you stand a chance of inadvertent damage of whatever type, whether you leave a tool behind or, without knowing it, step on a wire bundle or a tube.”

In one of the most historic shuttle-era photographs ever taken, this image shows the STS-38/Atlantis stack (at right) returning to the Vehicle Assembly Building (VAB) for repairs on 9 August 1990. In doing so, it passed the STS-35/Columbia stack (at left), which was returning to the launch pad after several weeks of extensive repair work on its hydrogen disconnect hardware. Photo Credit: NASA

Prior to the disaster, the shortage of spare parts had no serious impact on flight schedules, noted the Rogers report, but further cannibalism was “possible only so long as orbiters from which to borrow are available. In the spring of 1986, there would have been no orbiters to use for spare parts. Columbia was to fly in March, Discovery was to be sent to Vandenberg [Air Force Base in California] and Atlantis and Challenger were to fly in May.” Indeed, KSC’s shuttle engineering chief, Horace Lamberth, predicted that, had 51L flown successfully, the entire schedule would have been brought to its knees that spring by the spare parts problem alone.

Compounding the problem,” the report explained, “was the fact that NASA had difficulty evolving from its ‘single flight’ focus to a system that could efficiently support the projected flight rate. It was slow in developing a hardware maintenance plan for its reusable fleet and slow in developing the capabilities that would allow it to handle the higher volume of work and training associated with the increased flight frequency.”

With the loss of Challenger, all shuttle missions were suspended until the Rogers Commission—whose panel included former astronauts Neil Armstrong and Sally Ride, under the chairmanship of former Secretary of State William Rogers—had finished its work and made its recommendations. Among its conclusions were that NASA and Thiokol’s operation of the shuttle was seriously flawed. Concerns from individual engineers were not reaching appropriate managers, “critical” items were not given the attention they demanded, and the need to stick to a “schedule” was grossly overriding “safety.”

Astronaut Sally Ride was one of the members of the presidential Rogers Commission, established to investigate the cause of the tragedy. Photo Credit: NASA

Not only was NASA attempting to accommodate its major customers but, evidenced in a teleconference with managers at the Marshall Space Flight Center and KSC on the evening of 27 January 1986, Thiokol showed that it was prepared to ignore the safety concerns of its engineers in order to accommodate NASA, its own major customer. Worries of potential O-ring failure in the near-freezing weather conditions predicted for the following morning, as expressed by Roger Boisjoly and others, were downplayed, and Thiokol collectively voted that Challenger was fit to fly, unwittingly signing the death warrants of the seven-member 51L crew: Commander Dick Scobee, Pilot Mike Smith, Mission Specialists Ellison Onizuka, Judy Resnik, and Ron McNair, Payload Specialist Greg Jarvis, and the first citizen in space, schoolteacher Christa McAuliffe.

During that fateful teleconference, Bob Lund argued that his team’s “comfort level” was not to fly SRBs at temperatures below 12 degrees Celsius (53 degrees Fahrenheit) for fear of catastrophic “blow-by” of the O-rings and field joints, but he could present no evidence to Marshall that “proved” it was unsafe to do so. In a lengthy debate, Lawrence Mulloy—based in Florida as Marshall’s KSC representative at the time—and other NASA officials challenged Thiokol’s data and questioned its logic. At one stage, Marshall’s head of science and engineering, George Hardy, remarked that he was “appalled” at the company’s decision. So was Mulloy, who scornfully exploded with “For God’s sake, Thiokol, when do you expect me to launch? Next April?”

Neither man, however, was prepared to ignore the recommendation of their major contractor. Lund stood firm and, had he continued to do so, NASA would have had little choice but to postpone the 51L launch. Shortly thereafter, Thiokol requested a five-minute recess from the teleconference to consider the situation. Five minutes ultimately became half an hour. Throughout this recess, Boisjoly and fellow engineer Arnie Thompson continued to argue that it was unsafe to fly outside of their proven field joint temperature range, but the Thiokol senior executives in attendance felt the O-rings should still seat and function properly, despite the cold weather.

Freezing conditions, as evidenced by large concentrations of ice on Pad 39B, were co-conspirators in Challenger’s destruction on 28 January 1986. Photo Credit: NASA

Arnie actually got up from his position and walked up the table, put a quarter pad down in front of the management folks and tried to sketch out once again what his concern was with the joint,” Boisjoly told the Rogers Commission, “and when he realized he wasn’t getting through, he stopped. I grabbed the photos and tried to make the point that it was my opinion from actual observations that temperature was indeed a discriminator and we should not ignore the physical evidence that we had observed. I also stopped when it was apparent that I couldn’t get anybody to listen.”

Then, executive Jerry Mason explicitly asked Lund to remove his engineering hat and put on his management hat. When the teleconference resumed, Lund changed his vote and Thiokol changed its position on the issue. The company’s new recommendation was that, although frigid weather conditions remained a problem, their data was indeed inconclusive and the launch of 51L should go ahead the following morning. None of the engineers wrote out the new recommendation—“I was not even asked to participate in giving any input to the final decision charts,” Boisjoly told the Rogers hearing—and only the executive managers signed it. However, when Marshall and KSC managers asked for any additional comments from around the Thiokol table before closing the teleconference, none of them voiced their concerns. Boisjoly, in particular, remained silent—a fact which would later lead some observers to brand him a witness who turned “state’s evidence,” rather than a noble “whistleblower.”

When questioned by a Rogers panel member, he emphasized that “I never [would] take [away] any management right to take the input of an engineer and then make a decision based upon that input, and I truly believe that. There was no point in me doing anything any further than I had already attempted to do … [but] I left the room feeling badly defeated. I personally felt that management was under a lot of pressure to launch and that they made a very tough decision, but I didn’t agree with it.”

Challenger’s final crew, as they should be remembered: Positive and brilliant individuals, happily striving to explore space and further humanity’s reach into the Universe. In the back row (left to right) Ellison Onizuka, Christa McAuliffe, Greg Jarvis and Judy Resnik. In the front row (left to right) Mike Smith, Dick Scobee, and Ron McNair. Image Credit: NASA

Having analyzed the results of the teleconference, and interviewed the participants, the Rogers report concluded that “there was a serious flaw in the decision-making process leading up to the launch … A well-structured and managed system, emphasizing safety, would have flagged the rising doubts about the Solid Rocket Booster joint seal.” In fact, when brought to testify before the panel, key officials intimately involved with the decision-making process, including Launch Director Gene Thomas and Associate Administrator for Space Flight Jesse Moore, admitted that they had not been privy to the issues raised at the 27 January teleconference.

Over the years, many observers have commented that, had Challenger not been lost, another unsuspecting shuttle crew would have fallen victim to catastrophe. Astronaut Bob Parker, who would have flown aboard the next flight, Mission 61E, has expressed his fervent belief that disaster may have befallen himself and his crewmates … for the weather conditions in Florida in the early hours of 6 March 1986 were even colder than those on the night before Challenger’s fateful flight. Although it seems unlikely that Columbia could have been ready in time, NASA was still aiming to launch 61E at 5:45 a.m. EST on the 6th, kicking off an ambitious science flight with the ASTRO-1 payload.

Schedule pressure and the need to revise managerial communications channels to enable individual engineers to express concerns more openly were only part of the problem. On the technical side, decreed the National Research Council’s shuttle audit committee, the most important requirement was the redesign of the SRB field joints and O-ring seals to prevent future leakages. In its July 1986 response to President Reagan and the Rogers Commission, NASA announced a $680 million plan: to redesign the joint’s metal components, insulation, and seals, thereby providing “improved structural capability, seal redundancy and thermal protection.”

During the post-Challenger down time, Morton Thiokol’s Solid Rocket Boosters were subjected to a rigorous redesign process and underwent several test firings to recertify them for the Shuttle. Photo Credit: NASA

New capture latches would reduce joint movements caused by motor pressure or structural loads, and the O-rings were redesigned to not leak under structural deflection at twice the expected level. Internal insulation was modified with a deflection relief flap, rather than putty, and new bolts, strengtheners, and a third O-ring were added. External heaters with integrated weather seals would ensure that future SRB joint temperatures did not fall below 24 degrees Celsius (75.2 degrees Fahrenheit) and prevent water from entering the seals. “The strength of the improved joint design,” read NASA’s reply to Reagan, “is expected to approach that of the [SRB] case walls.”

By the time the shuttle returned to flight with STS-26 in September 1988, the redesigned vehicle boasted many end-to-end modifications which rendered it perhaps the safest it could possibly be. For more than a decade, crews supported dozens of successful missions and, with a number of exceptions, the SRBs functioned without incident. On the morning of 16 January 2003, an apparently routine flight—STS-107—lifted off to begin a 16-day science mission. Two weeks later, through a disturbing combination of cruel fortune and poor decision-making, Columbia was lost with all hands during re-entry … and the shuttle came to be recognized for what it truly was: a remarkable machine, capable of remarkable things, but an inherently unsafe vehicle. And in July 2011, bowing to presidential recommendation, NASA flew its final shuttle flight and closed out 30 years of astonishing achievement.



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  1. A chilling and sobering reminder of one of the saddest days of spaceflight. One wonders what the initial design philosophy of the SRB’s was as compared to the liquid, throttable 4-booster concept of the Soviet Energia/Buran vehicle. Again, an excellent 2-part historical posting.

    • “One wonders what the initial design philosophy of the SRB’s was as compared to [liquid-fueled boosters]”

      Cost. NASA managers – under pressure from OMB – ultimately decided (in 1971-72) that they couldn’t afford to develop liquid boosters on their development budget. MSFC resisted the idea for a long time; but in the end, it was an economics decision by an agency which feared its very existence was at stake if the Shuttle was not approved.

      See particularly chapter 9 of “The Space Shuttle Decision,” and especially the table on p. 420 comparing development costs for various pressure fed booster designs versus solids – link: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19990056590.pdf

      “Within the OMB, Daniel Taft, who worked with the NASA budget, saw an opportunity-and smelled a rat. The opportunity existed because NASA’s own estimates proposed that a suitable solid rocket motor would cost up to a billion dollars less to develop than a pressure-fed booster. In addition to this, the Air Force had already developed the 120-inch solids of the Titan 111, thus providing a base of experience along with confidence in the validity of the new cost estimates for solids. Pressure-fed versions carried no such experience and no such confidence, for they had never been built before.” (p.417)

  2. RE: “and the [other] seal had 24 percent of its diameter burned away. Sixty-one millimeters had been burned away. All of that destruction happened in 600 milliseconds and what was left of that last O-ring, if it had not sealed the crack and stopped that outflow of gases—if it had not done that in the next 200 to 300 milliseconds—it would have gone. You’d never have stopped it and we’d have exploded”…

    Not to downplay the seriousness of this erosion event, but it seems to me that even if the joint failed in 200-300ms it would be several seconds, (maybe up to a minute?), before any flame impingement would have burned through the ET. I am basing this on the time line of 51L.

    Just something I noticed…

    • The irony being that it wasn’t even cheap in the end. The corners cut in development led to extreme costs in operation. If it could have been understood early on that there wouldn’t be enough money to do that design right, it would have been technically possible to build a simpler or smaller vehicle on the funds available. I say technically possible because politically possible is a totally different discussion.

      A pair of Saturn F1s provides similar thrust to an SRB, and the J2 was a known upper stage engine for instance. Not developing the SSMEs and SRBs should have freed up funds to improve the operability of the vehicle. If less expensive to operate, some of the operational budget could have been available for constant serious upgrades. Technically of course, in political reality, no way. So a vehicle that was neither cheap nor safe was the flagship spacecraft for three decades.

      • “The irony being that it wasn’t even cheap in the end. The corners cut in development led to extreme costs in operation.”

        All very true. But it was a politically adroit move on NASA leadership’s part, because they realized full well that it’s much easier to kill initial political approval for a program than it is to pull the program on it once it’s underway. They knew that operational costs would be higher; and they felt fairly confident there would be cost overruns. But they were able to deliver a development budget in 1972 that hit the Nixon OMB’s magic target of under $5.5 billion.

        It is easy to look back at the What-if design scenarios that were rejected, such as the so-called “Flax Shuttle.” But one has the sense after reading the histories of the Decision that by late 1971 NASA leadership had boxed itself into the design they more or less had settled on; and with Apollo rapidly winding down, they felt they were running out of time and options. Going back to the drawing board to re-conceive a reusable Shuttle architecture (or anything else) looked very risky to the agency’s future, or at least its HSF program’s future.

      • ” The irony being that it wasn’t even cheap in the end. ”

        The program cost was $195bn. If every launch was at max nominal capacity, it would have cost $25,000/Lb of payload. Since they were not at max capacity, it was far more of course, and if I recall 17 people died as a result of how the program was managed. There was no cheap there, except in outcome.

        I was 14 and home sick from school, I watched the disaster live. I remember mention made of an Iranian ship downtrack, and speculation they might have something to do with it…

        Later, I remember rage which has not cooled to this day that it was colorably criminal negligence that killed them. When I have been the Engineer for Scout’s Merit Badges, I have given, “Take of your engineer hat and put on your management hat.”, as an example of what an engineer must never do. If any of them are engineers, I pray they never do.

        ” So a vehicle that was neither cheap nor safe was the flagship spacecraft for three decades. ”

        There is no irony, only 2 + 2 = 4 consequence, that it cost so much they could not afford safety or performance.

        To this day I can’t watch the whole footage of either Shuttle catastrophe, they make me too angry.

  3. John. You are correct. The F-1 and J-2 were proven technology and why NASA chose to ignore such a simple solution is beyond comprehension. Yes, technology clashed with the political and the political won out. Lessons learned?

    • 1) “The pressure-fed ocean-recovered boosters originally specified for the Shuttle could have used these engines minus the turbopump machinery.”

      But every pressure-fed design NASA looked at was pricing the total development budget out at over $6 billion (all of which were certainly lowballing it). Not least because recovering anything from the ocean means dealing with salt-water damage. There were more unknowns with pressure-fed designs, since NASA and its contractors had less experience with them – and that means more cost an schedule uncertainty.

      OMB Director Caspar Weinberger had been blunt with NASA: The Shuttle development bill needed to come under $5.5 billion. Fletcher had no pull with Nixon to get that number increased. And Nixon had to face a hostile Democratic-controlled Congress with key figures like Proxmire and Mondale who wanted to pull the plug on the whole thing.

      We can see the weakness of the SRB decision (as with so much else about the Shuttle architecture) clearly now. But at the time, the politics really handcuffed the decision badly. NASA in 1972 was facing a real prospect of having no human space flight program after the last of the Apollo hardware was used up. I’m not sure people realize how close we came to having that happen.

      2) “Musk and Bezos failed the genius test by not going straight to the 1972 TRW study as a guide.”

      This is the equivalent of saying “Musk and Bezos are not geniuses because they are not developing rockets the way I would.” But given that Musk has built three successful multi-billion dollar companies from ground up and that Bezos has made himself the richest man in the world by building Amazon from scratch, methinks there’s more than one test of genius.

      Musk’s long-term goal is indeed (also) to establish humanity off-Earth. We can argue about the wisdom of his plan for that (I share a lot of your skepticism about Mars in this regard, Gary). But his more immediate goal was to build a successful and competitive launch company on rather limited funding. Well, in just fifteen years he’s gone from a dozen guys and an empty office building to putting more payloads into orbit in the last year than either Russia or China did – and reshaped the entire global launch market even BEFORE he’s begun realizing the lowered costs of true reusability. In short, he succeeded in doing exactly what he set out to do.

      • I’m a space advocate. I want to see humanity expand out (permanently) into space, to explore its wonders, and develop its economic potential.

        I admire something things about what SpaceX does and how it does them, but it’s just a means to that end.

        Look, we know your feelings on all this. I’m not advocating you be kept from saying it again. But look: all most of us can do is express ourselves online, give our two bits to advocacy organizations. Meanwhile NASA has remained in a state of drift, stuck (as you put it) in Low Earth Orbit for almost five decades now. No matter how much we wish it, NASA is still years away from changing that. And that is because the vast majority of our fellow citizens don’t care about it, which means their elected representatives don’t care, either. At least entrepreneurs like Elon Musk, Jeff Bezos, Jeffrey Manber, and Robert Bigelow are trying to DO something about it, however modest those efforts look for the long term goals we all share.

    • @ Tom Vasiloff,
      To me, lessons learned are that there are three elements to the success or failure of a system. Politics, finance, and technical. When feasibility is multiplied out, financepoliticstechnical, each of the elements must have a positive element. What I suggested had a negative in the political feasibility place which makes it infeasible. I was suggesting from hindsight and likely wouldn’t have done any better with the information at the time. Equally, negative financial or technical aspects doom a project. Lesson is to make sure, to the extent feasible, that all three elements have a positive sign.

      The ignoring of the financial aspect as critical in Shuttle development is in a similar manner as many of the Mars now arguments. The current flagship thought seems to be to send 100 settlers at a time to Mars at reasonable cost. I don’t see the reasonable cost at this time. Using all round numbers that can be modified as one likes, say a billion dollar spacecraft is used to send the 100 settlers. That vehicle can only make one trip every other launch window so every four years and change years. Interest alone on a high risk billion dollars should be at least 10% (more like 20-30%). That’s four hundred million dollars in Interest Alone on each trip. Four million per settler is interest on the spaceship investment alone, and does not include payment on principle, development costs, launch, or gear for ground operations. I do not see settlement of Mars being financially feasible at this time with the information I have available. I believe that Shuttle lessons learned should apply here.

      Politics is another category. I believe that proper space development will not take place until private companies are carrying the load with private money. As long as government (taxpayer) funds are used, political feasibility will have to be addressed. That is both why the SLS/Orion is being developed, and why there is backlash at commercial encroachment of their turf. This is political feasibility vs financial feasibility.

      Technical feasibility properly is subordinated to the other two categories. There are many feasible technical solutions and uncountable infeasible technical ideas that cannot and should not be pursued
      unless one or both of the other factors gives good enough reasons.

      Hopefully lessons learned will be applied and not waved off. Sorry for the ramble, this is an important subject that I don’t necessarily communicate well.

    • The F1 was designed to operate at 1,000 psi or so and pressure feds tend to optimize around 300. Using the F1 thrust chamber in a pressure fed variant would require 1,000+ psi propellant tanks. Tank mass scaling with pressure, the tanks would mass over 3 times that of a designed pressure fed stage and engine. Eliminating the turbopump is possible at the expense of a mass ratio that destroys payload capacity.

      I think a more productive line of inquiry would be into the exact reasons why the proposed pressure fed boosters were projected to be so expensive. It seems that they should have been cheaper, and it would be interesting to know why not.

      • @John Hare:
        “Now -the only conceivable way to get that propellant mass flow rate into your F1 engine derived pressure fed booster, is to have an elaborate, massive, full flow, heat exchanger surrounding the combustion chamber/nozzle (sort of an expander cycle ON STEROIDS) for autogenous pressurization of MASSIVE heavy walled propellant tanks. This is laughable.”

        This may be a little fun exercise in my copious(ha ha) spare time. Intuitively, I kinda doubt this can be done, but you know “Analysis without numbers is only an opinion”.
        I’ll bet that in order to get steal enough gaseous O2 from the prop flow to get F1 “power pack equivalent flow”, you’d get so much pressure drop and heat loss that the engine won’t work -at all. Again, visulize a secondary LOX loop surrounding the combustion chamber/nozzle to tap-off for tank pressurization. Yeah, kind of an issue using warm gaseous O2 to pressurize the RP-1 tank, details details.

        The alternative is a separate gas generator sub-system just for pressurization, maybe hydrogen peroxide? Can you deal with the H2O in the LOX tank, or have to separate it? Can you pressurize the RP-1 with O2 at HIGH pressure without big badda boom?

        Big ass tank of liquid nitrogen, then use hot O2 from engine heat exchanger to vaporize for pressurization?

        All solutions look heavy, complex (read expensive) and defeat the whole rational for a pressure fed booster. Who ya gonna call? ATK!

  4. “Sidemount was really what the Shuttle should have been but was murdered by an administration ordering the space agency onto a more “flexible path.””

    Sidemount remains one of the most intriguing of Shuttle ‘what-ifs’ to me – an architecture that made considerably more sense than the orbiter. There were, indeed, a number of intriguing possibilities for NASA to salvage something out of STS after Columbia. But Mike Griffin insisted on tossing most of it aside for something much more ambitious (Ares I/Ares V). And by the time he left office in January 2009, it was too late to salvage something else out of Shuttle – which, I think, was by design. The production lines were mostly shut down by that point. (95% of the vendors for parts for the external tank were terminated as early as 2006, for example.)

    • Hello Gary,

      If it wasn’t clear, I actually agree with your main point, as such – Sidemount made the most sense as a true SDHLV, if we were going to have one. (Something like DIRECT’s Jupiter being probably the best runner-up.)

      My only concern was that your use of the term “flexible path” seemed to lay the blame on the Obama Administration. I happen to loathe Obama, but I really think it is quite unfair to blame this missed opportunity on him. By 2009 (let alone any later!), it would have been far, far more difficult – and much more expensive – to try to salvage some of STS in Sidemount form. The production lines and vendors for the ET and SRB’s were pretty much gone (I recommend reading Wayne Hale’s posts on this subject – no one would know better than him), and trying to put them back together would have been nearly as difficult as trying to build a new launch system.

      The real opportunity window for Sidemount closed in 2005-06. Mike Griffin, whatever you think of him otherwise, wanted it that way. He wanted the door closed to both the Shuttle and and Shuttle Derived HLV as quickly as possible, and closed for good. He got his wish.

      • Well, Wayne Hale was the Shuttle Program Manager from 2005 to 2010.

        I’m gonna have to defer to his assessment on this, barring some pretty extraordinary disclosures to the contrary. But everything I’ve read has synced up with that.

        Am I saying doing a Shuttle Sidemount was impossible in 2009? No. Just one heck of a lot more expensive, and time consuming. Because you’d have to rebuild almost all of the supply chain at that point. Which kinda defeats the whole point of the thing.

        Look, beat up on the Obama Administration’s space policy in all sorts of ways. But most of the blame for the end of Shuttle – and any opportunity for SDHLV’s – has to be laid at the feet of the Bush Administration.

    • P.S. Think about it this way, Gary: What is the point of developing a Shuttle Derived HLV?

      I mean, if you were designing a heavy lift launcher from scratch, you’d never design it like that. No one would. (The DIRECT guys made this point repeatedly about their own SDHLV architecture.) If Gary Church/MichaelatNASA were doing it from scratch, he would not design it this way; he’d opt for a pressure fed liquid fuel booster, and…well, you know the rest.

      No, the rationale was to take maximum advantage of existing production lines, vendors, and human workforce to the greatest extent possible. Because it would save money, time and (yes) jobs.

      But if you try to develop it after those production lines, vendors, and human workforce have mostly vanished, it makes the whole exercise bootless, because that rationale is now basically gone.

      It is a great pity this possibility of a Sidemount (or even some other) SDHLV was never pursued while we had the chance. On that much, I believe we are in agreement.

  5. John: excellent points all and very thought-provoking. I agree that privatization will likely be a key component of any series of missions to Mars and beyond. Thanks!

  6. Well done retrospective by Ben Evans.

    All of these “coulda woulda shoulda” comments are predictable and of little utility -if we don’t learn going forward, from the Challenger accident. Are we? Maybe not.

    Case in point #1: Virgin Galactic. Following the deadly 2014 VSS Enterprise accident, I urged (implored) VG to build a pilot-less test airframe and get on with it. There were two of the world’s leading UAV conversion companies, literally within walking distance of VG in Mojave. Without human pilots at stake, VG could flight test the sh*t out of the airframe and its troubled hybrid engine, on an accelerated pace. Did they listen? Obviously not, manages insisted that this is a CREWED spacecraft and a UAV version just would not look right to the public. Sound familiar? Kind of like MSC in the 1970s?

    Case in point #2: SLS. The very first flight of the new EUS will be made with crew on board. And the EM-2 will be on the only second flight of the new SLS. Insisting that SLS be human rated from the get-go, has dramatically (dramatically -ridiculously) inflated the cost and schedule of the program, and will make it more risky for that first crew. Getting Déjà Vu.

    I have every confidence that the SLS will have a perfect operational record, but at what cost? People tend to not see the lost opportunity costs; important in-space technologies to make the missions safe and productive IN-space are being deferred to pay for the SLS/Orion “crew first, details later” program.

    • “The very first flight of the new EUS will be made with crew on board.”

      Which really is astounding.

      The Saturn V got two test launches in all-up mode.

    • Anybody,
      Please explain the need for a crew at this point considering the software capabilities that are taking over the planet. Cars and trucks will be driving themselves …The Airline industry has already said that all airline functions are automated which I believe because of the number of pilots who are caught drunk when they get on the plane.

      In looking at the VG video of the accident it looked intentional or the pilot really had no idea that putting on the brakes at max thrust would literally cause the craft to brake apart…

      The Soviets flew the Buran with software on its first flight in the 1980’s and landed it without pilots.

      • Having a crew or not depends on the objectives of the flight. If the objective is to send hardware somewhere, perhaps not. If you want development and settlement of space, including various solid bodies, people will need to be there. People need to be on site if they are to settle there.

      • The chief reason to emigrate from Earth to anywhere else is to get away from the control of people who want to run your life for you. Owing to the increasingly sophisticated AIs available to run drones and rovers, there is little need with the cost of space access falling so dramatically, to employ anything but AIs and remote control for the purposes of either exploration and exploitation of space, when done for the purposes of the people on the Earth.

        With the cost of access falling so dramatically however, and the interest in doing so as strong as it is, several tens of thousands at least will sell out and emigrate simply for the purpose of doing so. Then they will live there for their own purposes, as will most of their descendants.

Missed Warnings: The Fatal Flaws Which Doomed Challenger 32 Years Ago (Part 1)

On 60th Anniversary of Explorer 1, SpaceX Successfully Launches SES-16/GovSat-1 Payload to Orbit