Chair Force Engineer

Wednesday, May 23, 2007

What's Up, Dock?

It's recently been announced that the James Webb Space Telescope will be equipped with a docking ring for the Orion spacecraft. While the news brought me some initial excitement, I'm now scratching my head as to what's really going on within NASA.

The rationale for the Orion docking ring is simple: what happens if the spindly telescope fails to deploy properly? Before today's announcement, the answer would have been, "Say goodbye to $4.5 billion." The addition of the docking ring means that a human crew would have a fighting chance of manually correcting any deployment problems--or does it?

According to current schedules, JWST will launch in June 2013; a manned Orion/Ares I flight won't occur until two years later, according to current budgets and schedules. Further, Ares I will have nowhere near the delta-V to get Orion to the L2 point where JWST will reside. An Orion mission would likely have to wait until Ares IV (the hybrid of Ares I&V) is ready, which would probably be a few years beyond the projected 2015 flight of Orion with her first crew.

A bit closer to earth, a similar solution might make sense for the Hubble Space Telescope. During the projected 2008 Hubble Servicing Mission, Hubble will receive a low-impact docking system. While NASA's plan is to eventually de-orbit Hubble, a future Orion servicing mission shouldn't be ruled out.

If Orion docked with Hubble, the crew would be at a bit of a disadvantage using the stock Orion capsule. Without an airlock, the crew would have to vent the cabin every time an EVA was conducted. Crew members would also lack a platform to stand on while performing repairs.

The solution to these problems is an airlock module that was also equipped with a smaller version of the shuttle's CanadArm. The module would be stored in the spacecraft adaptor during launch; Orion would dock with it after reaching orbit. The airlock, in turn, would have a LIDS on its free end for docking with Hubble.

The airlock module is out-of-the-question for Orion flights on Ares I. There's no margin on that launcher, and the Orion service module acts as a third stage. However, if Orion was launched on a Jupiter 120, there would be up to 20 metric tons of payload margin that could be used for an airlock module, or even additional payload (replacement parts and upgrades for Hubble) mounted to Orion's service module. Even better, it's possible for Jupiter 120 to support a 2012 Hubble Servicing Mission.

It's possible that a Jupiter derivative could also reach JWST, but such a mission wouldn't occur by 2013 either. The Jupiter derivative for this mission would also require an upper stage to take Orion to L2 and back.

In short, outfitting JWST for an Orion repair mission doesn't make sense, unless significant delays are expected on JWST. Frankly, I wouldn't be surprised if big delays were in store for the next-generation telescope. An Orion mission to the venerable Hubble telescope would make a lot more sense, but NASA doesn't have a launcher that will be ready in time to perform the mission.