"3 Questions" gives members of the community the opportunity to sound off on current events in their field of expertise. Jeffrey Hoffman, professor of the practice in MIT's Department of Aeronautics and Astronautics, is a former space shuttle astronaut whose five flights included the first Hubble Space Telescope servicing mission in 1993.

He offered his thoughts on what the next repair crew can expect during the fifth and final Hubble servicing mission set for launch on May 11, and on NASA's future.

Q. What's the most difficult aspect of doing hands-on repairs in orbit on a giant, delicate instrument like the Hubble?

A. I treat it much the way I treat working on a car or any other type of home repair. The number one thing is, don't hurt yourself, and that kind of gets lost in the weeds sometimes, but the number one thing in human spaceflight is safety. Number two, don't break anything that isn't already broken. That happens sometimes during home repairs, and you curse and yell, but you can afford the time; you can't afford the time when you're up in space.

And then finally, you've got to fix the problem. And that is sometimes easy: Most things on Hubble were designed for easy access for space-suited astronauts. But there have been plenty of tasks that we've had to deal with that were never originally contemplated, and so you need skill at using a spacesuit and particularly fine manipulation with big bulky spacesuit gloves, and also an understanding of the tools you have, and the ability to come up with innovative solutions when problems occur.

Q. After all the months of training and simulations you went through, was there anything when you got out there that surprised you?

A. Oh yes, absolutely. We were of course expecting to be surprised. Every time NASA had visited a satellite before Hubble, there had always been surprises - usually due to something being out of configuration compared to the drawings.

Now the Hubble project did an extraordinary job of configuration control, so things were the way they were supposed to be, but not everything worked the way it was supposed to. Particularly, the first day, after we successfully replaced the gyroscopes, the door wouldn't close.

That was probably our biggest problem, and that could have destroyed the telescope had we not been able to get that door closed. It was warped, and we had to figure out a special way to use a tool - it was just something that had never been envisaged before, we had never trained for it. It was always assumed that we would just close the handle and the door would close. It didn't work.

We had a solar array that didn't roll up and we had to leave in orbit. We had an electronics box that we knew in advance we were going to have to replace; it was not designed for EVA [extravehicular activity] replacement, and there were all these tiny little 2 millimeter screws, which we were told were captive screws, but in fact in zero-g they weren't.

So they started floating all over the place, and we had to grab them and chase them all around, and it was a mess. That was right at the limit of what we were capable of doing in a spacesuit.

Q. What are your thoughts about the impending end of the shuttle program at the end of next year, and the possibility of extending it beyond that?

A. The shuttle is an extraordinarily capable vehicle. It's been very good to me, and I've done some extraordinary things with it. It was built under difficult circumstances, and so its design was compromised. It's far from a perfect vehicle.

The shuttle was designed specifically for low-Earth orbit, just to go up a few hundred miles and back. The shuttle itself is getting old, so the bottom line is I think it's time for a new vehicle. The shuttle was never as easy to maintain and refly as was originally imagined, despite the fact that it's extraordinarily capable once it's up in space.

It's a more dangerous vehicle than it should be. We know that. It has no escape system, it's sitting on the side of the stack rather than on top where well-behaved human-carrying modules should be. It's very capable, but it's not as robust as it could be.

Even at the beginning of the shuttle program, we were still dreaming about going back to the moon, and even farther, and the shuttle was never designed to do that. And we now have a new direction in the space program where we would like to do that. I hope that direction is continued by this administration. And so one way or another we need a new vehicle.

I think the tragedy is that we as a country, as an agency, waited until the imminent retirement of the shuttle to start designing and building a new vehicle. We've had several false starts over the last 20 years, and wasted billions of dollars, but that's the way it is, and here we are.

So I think it's the right decision to retire the shuttle. And given the fact that it's going to be retired I don't see any justification for keeping it flying for just a few more years. Yeah, so we have a gap in U.S. space capability.

The only thing we need a spaceship for during the next few years is to get up to the space station, but the Russians will do that for us, and maybe even Elon Musk [founder of SpaceX, which is building the privately-funded Falcon 9 rocket] will do that for us. In fact, I'd love to see private industry take over maintaining the low-Earth orbit infrastructure.

If private industry could support that on the basis of tourist travel and however else they can make money, then NASA could buy their services at the marginal cost of doing business instead of maintaining the whole infrastructure.

I mean, NASA spends a third of its budget just supporting a transportation infrastructure, and if that could be obtained from the private sector, NASA would save a lot of money, which could be used for exploration, which is what I think NASA's real goal should be in the future, not running a transportation system.