Wednesday, May 23, 2007

Will Astronauts visit Hubble's replacement?

If next fall's visit by astronauts is successful, the Hubble Space Telescope will be with us for at least another five years. But plans are already in place to launch NASA's next large space telescope, the James Webb Space Telescope, in 2013 (although I'd be surprised to see it launched that year).

Although the Hubble has been well-served by four (and soon a fifth) servicing missions by astronauts, we've always assumed that JWST would not be able to be visited by astronauts. Hubble is in low Earth orbit (just a few hundred miles up), where the Space Shuttle can easily fly. But the JWST is going to be at the second Lagrange point, a spot about 1 million miles away from the Earth where the Earth and the Sun's gravity balance perfectly. The main reason for this distance is to get the telescope, which will look at infrared light, far from the heat of Earth. But none of our current rockets can carry humans to this Lagrange point, so it seems that repair of the telescope is out.

So I was surprised today when NASA announced that it was going to add a docking port to JWST in case future astronauts ever visit the spacecraft. Their reasoning is that if this expensive telescope fails to work, their new Orion rockets might be able to take astronauts to the Lagrange point to try and salvage the telescope.

If astronauts were to go to the JWST, it would mark the furthest humans had ever ventured away from the Earth -- it is nearly four times further from the Earth than the moon. It would also be a very risky and very expensive mission. Would it be worth the trouble? I don't know. Certainly astronauts would probably like to try if the chance of success seemed reasonable, and I don't doubt their ability to fix the spacecraft.

But adding a docking ring adds weight and complexity to the telescope, two things that are not always desirable. I am not a space engineer, so I really do not know how much the docking ring affects the spacecraft. But it could also mean that some science may need to be scaled back to reduce the weight of the telescope. Again, this is just my guess, I don't know.

So, I have mixed feelings about the announcement. In some ways, I am glad NASA is thinking ahead and allowing for new possibilities we hadn't previously dreamed of. But I have reservations, and until I know more about the plans, I'll remain skeptical.

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