KENNEDY SPACE CENTER, FL – Under the Under NASA’s Commercial Resupply Services (CRS) contract, Orbital Sciences and SpaceX are each to be paid $1.6 billion to deliver 20 metric tons, or 44,100 lbs, of cargo to the International Space Station (ISS). Under the terms of CRS, SpaceX will conduct 12 missions and Orbital Sciences will launch 8 missions. As Orbital Sciences is on its first demo mission to ISS, this is a good time to review the status of the CRS program.
SpaceX has conducted one demo and two CRS missions to ISS. SpaceX’s COTS Demo 2/3 mission lifted-off on May 22, 2012, CRS–1, or SpX–1, on October 11, 2012, and CRS–2 on March 1, 2013. SpX–3 is not expected until mid-January 2014. Total delivered upmass by SpaceX to ISS to date, without packaging, is 1,519 kg (3,349 lbs).
Orbital Sciences is currently conducting its first demo flight of Orbital’s Cygnus robotic cargo spacecraft, which will rendezvous with, and then be captured by, ISS. Orbital’s first CRS–1 flight is scheduled for December 8, roughly 2 1/2 months from now, and will carry 1,288 kg (2,839 lbs) of supplies, not counting packaging, to ISS. Over the course of its CRS contract, Orbital will deliver on average 2,500 kg to the ISS over its 8 missions.
|Company||Mission||Launch Date||Unpackaged Cargo|
|Upmass (kg/lbs)||Downmass (kg/lbs)|
|SpaceX||COTS Demo||22 May 2012||520/1,146||660/1,455|
|SpaceX||SpX–1||8 October 2012||454/1,001||520/1,146|
|SpaceX||SpX–2||1 March 2013||545/1,202||1,045/2,303|
|Orbital Sciences||COTS Demo||18 September 2013||700/1,543||1,124/2,478|
|Orbital Sciences||Orb–1||8 December 2013||1,288/2,839||956/2,107|
|Orbital Sciences||Orb–2||8 May 2014||1,563/3,446||1,563/3,446|
The Dragon spacecraft weighs 4,200 kg (9,259 lbs) and can handle 3,310 kg (7,297 lbs) in both its shirt-sleeve pressurized volume and its unpressurized trunk for a total of 6,620 kg (14,595 lbs). The first generation OSC Cygnus spacecraft weights 1,500 kg (3,300 lbs) and the second generation Cygnus + that will be used after its the third Orbital Sciences CRS mission, Obs–3, weights 1,800 kg (4,000 lbs). Below is a table of pressurized volume and payload upmass capabilities of ISS resupply spacecraft.
|Spacecraft||Pressurized Volume||Pressurized Payload|
SpaceX’s CRS missions’ past payload upmass to date of 1,519 kg (3,349 lbs) means that future missions will need to be more heavily loaded. Certainly from its payload mass numbers, Dragon is up to the task. The Dragon’s pressurized volume of 11 m3 (388 ft3), 1 m3 more than the 1960’s era Apollo command module. From SpX-3 going forward, in order to fulfill the terms of its fixed-price CRS contract for the remainder of its term, SpaceX must deliver a total of almost 18,000 kg (roughly 41,000 lbs) to ISS. This means that the average Dragon payload mass will need to be around 1,800 kg (4,000 lbs) and would represent a significant increase in payload over past SpaceX CRS missions, though clearly not an amount that comes even close to Dragon’s payload capability.
As noted above, Orbital Sciences will also have a challenging time meeting the payload commitments of its CRS contract after Obs-2. From Obs-3 onward, Orbital Sciences will need to deliver around 15,500 kg (33,000 lbs) to ISS. This means that over the next six Orbital Sciences CRS missions, Cygnus must launch an average of 2,500 kg (5,500 lbs). While the standard Cygnus only carries 2,000 kg (4,409 lbs), the Cygnus +, which will see its debut beginning on Obs-3, has just the right amount of payload capacity of 2,700 kg (5,950 lbs).
After As a historical benchmark, Shuttle could easily lift 9 metric tons (20,000 lbs) to ISS, although it was, after introduction of the Al-Li 2195 external tank , capable of lofting nearly 13 metric tons (28,000 lbs) while maintaining its abort landing capability.
- Orbital Sciences–NASA CRS Contract ↩
- Orbital Sciences–NASA CRS Contract Modification ↩
- SpaceX–NASA CRS Contract ↩
- SpaceX–NASA CRS Contract Modification ↩
- SpaceX refused to clarify differences in nonpackaging payload upmass on it COTS Demo flight manifest. ↩
- SpaceX refused to clarify differences in nonpackaging payload upmass on it SpaceX CRS–1 flight manifest. ↩
- SpaceX refused to clarify differences in nonpackaging payload upmass on it SpaceX CRS–2 flight manifest. ↩
- Habitable volume for Dragon has not yet been published by SpaceX and is an estimate. ↩
- Unlike Dragon, Cygnus will not be crewed and does not have a “habitable” volume. ↩
- SpaceX Dragon Webpage ↩
- Supe Lightweight External Tank ↩