I'm Jeff Hoffman - former NASA astronaut and current MIT Professor. In my spare time, I'm the director of the Massachusetts Space Grant Consortium and Deputy Principal Investigator of an experiment on NASA’s Mars 2020 mission.

I've logged 1000 hours of flight time aboard the Space Shuttle, spent four years as NASA’s European Representative, and joined the MIT faculty in August 2001.

My free Introduction to Aerospace Engineering course on edX begins September 26th.

I'd love to answer any questions you have about outer space!


Here's my proof

Comments: 215 • Responses: 55  • Date: 

jjrf1816 karma

What do you think of SpaceX's proposed approach for getting to Mars?

What changes do you think need to happen (not just SpaceX) in order to safely get to Mars?

Do you think going back to the Moon will help us get to Mars or should it be treated completely separately? (I have heard plenty of people on both sides of this argument and am curious what your thoughts are)

jhoffma118 karma

I'm enthusiastic about it. However, Elon Musk now says that he has second thoughts about hypersonic retropropulsion for entry. He has said he will reveal his "new" plan at the IAC meeting next week, so stand by.

TheTrueLordHumungous15 karma

Ever seen a UFO? What do you think about the astronauts, like Gordy Cooper who have publicly come out with their accounts of what they believed to be non terrestrial UFO's? Thanks.

jhoffma123 karma

There are many things that you can see in space that are weird and you might not be able to identify. That does not mean that they are spacecraft piloted by aliens.

blastr4214 karma

Dr Hoffman, I watched your MIT Space Shuttle class (twice) and am very interested in space history (propulsion engineer!). Listening to you, Aaron Cohen and others, I've always wanted to ask this question: The Shuttle was a marvel that achieved all of its "technical" requirements, but failed to meet its flight rate and ease-of-reusability goals. At what point during the development of the system did the engineering team realize the shuttle wouldn't "work" in the sense of flight rate/reusability? What was the reaction of the program management? Was a decision ever conscientiously made to simply get the current design flying and try better the next time around?

jhoffma13 karma

This is too complex a question to deal with simply. The Space Shuttle course is now being prepared as a MITx course which will be given in the fall of 2018. We will discuss this more fully at that time.

mpkessler7 karma

What would be the most useful simple resource to send up to LEO on the Falcon Heavy test flight? For example, would sending up water be the greatest benefit for future spaceflight?

jhoffma18 karma

When we go to Mars or the Moon, we will need a lot of water and oxygen. However, paying to launch all of this from the surface of the earth with SLS or Falcon Heavy is a waste if we can obtain them from local resources. This is the idea behind ISRU - in situ resource utilization. Learn to live off the land, which is what most explorers hae always done.

hellzkeeper12167 karma

Seeing the Earth from up there and realizing what a rare thing our planet is, do you believe there are other planets that could support intelligent life? 

jhoffma126 karma

There are so many planets in the universe that it is almost certain that life exists in many places. However, whether any other life forms have evolved into what we would recognize as "intelligent" is something we can only speculate on.

Vikrantvicky04137 karma

What do you have to say about India's latest launch of 104 satellites in one go? Also what are your views about the future of ISRO in manned missions?

jhoffma15 karma

India has a very serious space program. It started out just aimed at economic benefits for India, but now it includes many scientific missions. India has expressed a desire to develop the capability for human spaceflight. I hope they are successful.

demonicpigg6 karma

What's the most interesting experiment that you were a part of aboard the space shuttle?

jhoffma121 karma

On my last flight (STS-75 in 1996) we deployed the tethered satellite, a 1.5 m diameter sphere that remained attached to the shuttle by a 20 km long wire. Looking up at the wire disappearing into space, I felt like Jack looking up at the beanstalk!

custom_user5 karma

Do you think that Boeing and SpaceX will make it and provide astronaut transportation in 2018? Or there will be delays?

jhoffma15 karma

It looks like it may well be 2019 before they are all certified and ready to go. Stand by...

Astro_Neel4 karma

I'd love to hear your thoughts/comments about what should be the first landmark for expanding our society out in the solar system- Mars or the Moon?

jhoffma14 karma

Mars is a long-term goal, but the Moon is a lot easier to get to. I think it would be a good idea to test out many technologies for Mars on the Moon.

vjimenezq3 karma

Hello Mr Hoffman. What do you think about plasma engine that Franklin Chang-Díaz astronaut has been developing?. They say it could take us to Mars in 40 days.

jhoffma13 karma

I flew with Franklin twice, and I am familiar with his work. It is very exciting and has incredible promise if it can be proven to work. So far, he has made great progress. I hope to see a test of VASIMR on the ISS in the not too distant future. Improved propulsion is critical for our future in space, and this is one of the technologies that could provide this.

benjaminperdomo3 karma


What do you think about SLS and Orion?


PS: I just loved the Introduction to Aerospace Engineering course when I took it. Really great.

jhoffma15 karma

Thanks for your kind words about 16.00x SLS and Orion are NASA's new rocket and space capsule. They will be very capable but are quite expensive. I reserve judgement until we see them in action. That's the real test of any space system.

Xene1042_Genesis3 karma

Would you fly to space again (for example to the ISS) if you were offered to do so?

jhoffma110 karma

I'd go in an instant (but please don't tell my wife, who is happy that I am not flying anymore!)

a_unique_username883 karma

When did you know you absolutely wanted to be an astronaut?

jhoffma17 karma

When I was 6 years old. However, all the early astronauts were military test pilots, so I never considered being an astronaut as a realistic career goal. When the shuttle came along, however, there was a crew of 7 and they only needed 2 pilots, so that opened up opportunities for scientists and engineers.

stepo3553 karma

Hello! Here's Stepan, 22 y.o. from Czech Republic, STEM major. My question you think that our generation will have better affordable opportunities to visit space? Now you have either be an astronaut or pay $20M to go to ISS. Do you think that Musk's $200K Mars-rountrip-vision is real? Do you think that Branson's project will be affordable? Thank you have a nice day!!

jhoffma13 karma

For now space travel remains extremely expensive. SpaceX and Blue Origin are working hard to make it less expensive, but it will be a long process, and I don't know when space travel will become a reality for lots of people. Transatlantic airplane flight was extremely expensive when it first started, and it took several decades and the development of commercial jets to bring the cost down to where it is today.

AstronomyLive3 karma

What are your thoughts about the recently announced framework for returning samples collected by the 2020 rover and how realistic is the proposed timeline for getting those samples back to earth?

jhoffma16 karma

I have an experiment on the 2020 rover - MOXIE - which will produce oxygen using local Mars resources (ISRU). So I am familiar with the caching system that Mars2020 will use. All the Mars2020 scientists are excited that it now looks like the cached samples will actually be returned to Earth. Mars sample return has been at the top of the planetary science priority list for many years. It's great that NASA is now preparing to do it.

jbaugh9302 karma

I'm a sophomore majoring in aerospace engineering. What steps would you recommend taking to become an astronaut?

jhoffma12 karma

Study hard, get good grades, and get a good job where you can distinguish yourself. If you are lucky enough to get selected as an astronaut, that's great. But if not, at least you will have a rewarding career.

Diana-LFS2 karma

Is it posible to become an astronaut at 40 Professor?

jhoffma13 karma

There is no "official" age limit for astronaut candidate selection. NASA has selected a few astronauts in their early 40s. Other than John Glenn, who flew at 77, the oldest astronaut to fly was in his early 60s.

RishikeshJani2 karma

What significant breakthrough could we get in the field of aerospace engineering in the near future? What breakthrough would you like to see happen in the near future? What does being in zero gravity actually feel like?

jhoffma15 karma

I think our two biggest needs are better propulsion (get to places faster) and protection against radiation.

Zero gravity is a real blast. It's a feeling of physical freedom like I never experienced anywhere else. I think it is so much fun that people will pay to experience it - space tourism.

mpkessler2 karma

Why have we not seen trials of centrifugal artificial gravity in orbit yet? What are the challenges of such a test?

jhoffma12 karma

There was a centrifugal tether test done during the Gemini program, but that was the only time. We have concentrated on learning how to keep people healthy without gravity. If this proves impossible over the long times required to go to Mars, then centrifugal artificial gravity is always available as a backup. However, these systems will be more massive, and hence more expensive.

obnoxiouscarbuncle2 karma

Do you have a meal that you like to cook at home?

jhoffma15 karma

My wife does most of the cooking, but I love a good New England lobster, and I am responsible for cooking the lobsters.

4pply_yourself2 karma

What was the greatest adversity you faced during your time in space? How did you address it?

jhoffma15 karma

The most critical mission was the rescue/repair of the Hubble Space Telescope. On the first day, after replacing the gyroscopes, the main door would not close, which would have doomed the telescope. It took us an hour to figure out what the problem was and how to solve it, which involved using a standard tool in an unconventional way. But that's what astronauts are supposed to do - solve problems.

AguirrePiera2 karma

Do you think LARGE scale, high thrust ion engines and/or nuclear rockets have potential for the future of in-space propulsion?

jhoffma13 karma

Better propulsion is critical to reducing travel times, which reduces logistic requirements and radiation exposures. NASA is funding some research in high thrust ion engines as well as nuclear thermal rockets, but we are still pretty far away from having usable systems.

Pottss252 karma

Do astronauts train on the vomit comet? How does the vomit comet compare to space vs. the buoyancy lab? Thank you

jhoffma11 karma

The 0-g aircraft produce real weightlessness, which is just like being in space, only for a very short time (20-25 seconds for each parabola). The neutral buoyancy lab is great for EVA training, but you are not really weightless.

powerscunner2 karma

I imagine that lots of stuff gets loose and travels around the cabin in zero-g, so my question is what's the most surprising thing you found floating in front of your face?

jhoffma15 karma

The most surprising thing that anyone found floating in front of his face was, I think, his own hand! When you are weightless, you can lose track of your arms and legs if you are totally relaxed. A sleeping astronaut awoke to see a "mysterious hand" floating in front of his face. It took quite some time for him to realize that it was his own hand!

Xene1042_Genesis2 karma

What do you do when something dusty or anything like that starts floating around? How do you stop it prom hurting people or damaging stuff? Thanks!

jhoffma15 karma

Dust in space is a real problem, because it doesn't fall to the ground. The air is constantly circulated through filters to remove dust and lint, but we need to be careful to minimize the amount of dust created - for example no woolen clothes (lint) and no cashew nuts (too many crumbs).

punyeta_ka2 karma

I have red from a NatGeo book that space smells like a steak? Is it true?? How does it smell?

jhoffma15 karma

I never sensed a smell after coming in from a spacewalk. Some astronauts say they sensed a "metallic" smell. I never heard anyone say it smelled like steak.

GalacticAstronaut2 karma

Is there any particular message you like to give to students to inspire the about STEM / space travel / Spaceship Earth? (I'm signed up to fly into space on a suborbital flight with Virgin Galactic and am doing student outreach; I've been leading astronomy lessons in classrooms in volunteer programs since 1995). Thanks, and thanks also for MIT 16.885 & 16.00X online- fabulous stuff!

jhoffma15 karma

STEM is what has allowed humanity to progress from the stone age to the space age and will propel us into the future. If you want to be part of this, you need STEM knowledge. Even if you are not developing the new technology or science, it is important to be able to understand the complex technical world in which we live. And it's FUN!

wec98871 karma

Do you advocate sending humans back to the moon first, and then to Mars, or just going straight to Mars? Any thought of building a space station at a Lagrange point to use as a starting/assembly point for Mars flights?

jhoffma12 karma

Please check out NASA's web site to look at current plans for cis-lunar development, which will address all of these questions.

massterchieff1 karma

Aerospace Engineering and Space Craft Engineering - are they the same thing?

jhoffma15 karma

Aerospace engineering is more general - it involves rockets, satellites, spaceplanes, etc. Spacecraft engineering would generally refer to satellites or planetary probes.

PickleChomp1 karma

I currently work in IT with a BA degree in computer science. I'd like to take this edX course as a first step in transitioning to hard rocket engineering. What should my next steps be?

jhoffma14 karma

Next fall (2018) MITx will have a new course that I am putting together on Space Shuttle Engineering. That would be a good start. However, if you are serious about a career in aerospace engineering, you need to consider a graduate program where you can get a masters degree. Good luck!

slaura19951 karma

Dr Hoffman, what kind of material was used for the Space Shuttle thermal protection system? It was only ceramic materials or ceramics matrix composite with silica fibers?

jhoffma13 karma

The tiles were ceramic. There were also thermal blankets on cooler parts of the shuttle and there was carbon-carbon on the hottest parts like the nosecone and wing leading edges. This will be covered in the fall 2018 MITx course on Space Shuttle Engineering

mollsoherman1 karma

What is it like to watch storms from space? The hurricanes hitting the Caribbean and South Eastern part of the USA must be incredible to watch from up there!

jhoffma14 karma

Seeing lightning from space was the greatest light show I have ever seen!

wec98871 karma

I signed up for the course. Any recommended pre-course studying?

jhoffma13 karma

The course is self-contained, but the more you have read about space exploration and space travel, the more you are likely to get out of the course. I hope you enjoy it!

Pottss251 karma

I recently saw a video where a water balloon was popped on the space station. Do the small droplets that shot off attract back to each other or just continue on the trajectory until they attach to a surface?

jhoffma12 karma

If two water droplets touch, they will cohere and stick. But once they are on an outbound trajectory they will continue. There's nothing pulling them back.

yassine91kan1 karma

When have you noticed using electrical power as propulsion for the spacecraft during the flight?

Do you ever think that we can fly a spacecraft using electrical power as a main source of power for the engines to push towards electric mobility?

jhoffma11 karma

Many small spacecraft (planetary probes) already use electric propulsion (i.e. ion drives). The problem is that they have low thrust, so they are not yet suitable for human spaceflight, where you want to get places as quickly as possible.

Diana-LFS1 karma

What would be your main piece of advice in terms of setbacks, for someone willing to become an astronaut Professor?

jhoffma13 karma

Becoming an astronaut is a wonderful dream and can be very motivating, however the chances of selection are slim because so many people apply. For NASA's most recent selection, 18,000 people applied and only a handful were selected. So my advice when people ask me this question is that becoming an astronaut should be your "Plan B", and you need to have a good "Plan A". In other words, pursue a career in which you are interested and competent, and keep applying to the astronaut corps. Good luck!

_bobby_tables_1 karma

Do you ever think ramjet technology can be made practical?

jhoffma12 karma

I think you are referring to hypersonic airbreathing propulsion. Many countries are working hard on this. I am sure someday it will become feasible.

Phantom08091 karma

Do you think we should explore terraforming of planets like venus and mars before fully exploring them? More broadly speaking, do you think space is ours to spoil?

jhoffma18 karma

Terraforming is way beyond our technical capabilities at this time. I don't want to see us "spoil" space, but extending life beyond the Earth is, for me, an ethical imperative.

corokdva1 karma

Dr. Hoffman first of all congratulations for the amazing course and thank you for taking the time to answer.

As someone who's taken the Intro course already I would love to continue my studies, especially on Rocket Engines, Orbital Mechanics, Spacecraft and Mission Design. Do you plan on offering new additional courses in the future? Are there any in the platform that you personally recommend?

Thank you.

jhoffma12 karma

I am putting together a course on Space Shuttle engineering that will be given on MITx in fall 2018.

slaura19951 karma

Dr. Hoffman, how long will be the travel from Earth to Mars?

jhoffma11 karma

With current propulsion technology, about 8 months each way.

cbrian131 karma


jhoffma12 karma

The Neutral Buoyancy Facility (Water Tank) where we practiced EVA was my favorite.

rishabhc071 karma

Is there any life possible on Mars for normal people like me?where oxygen level is 0.1% and water only present in form of vapour or ice.

jhoffma11 karma

Not for normal people like us. However, there are bacteria on Earth that survive in incredibly hostile environments, even way underground. If similar life ever developed on Mars, it might still be able to survive underground.

NixUsr01 karma


What is your opinion on AI and its application in the missions?

jhoffma12 karma

AI has been applied to a lot of mission control tasks already. It's hard to answer your question without a good definition of what you mean by AI. Computers already control a lot of time-critical operations, but that isn't what we normally mean by AI. At present, we don't have AI systems making life-critical decisions.

MarioPol1 karma

So... what does an aerospace engineer exactly do?

jhoffma13 karma

Design, build, test and operate aerospace systems, which means airplanes (piloted and drones), rockets, satellites, planetary probes and anything else that leaves the surface of the Earth. I like to tell my students that aerospace engineering is what gives us the freedom to move in the third dimension (up and down).


What does space food taste like?

jhoffma15 karma

It's a lot like backpacking food. Mostly dehydrated or MREs. The Russians use a lot of canned food. It's pretty gooey. Your sense of smell is decreased in space, probably because of all the extra fluid in your head. NASA gave us lots of hot sauce to spice things up. When I got back from my flights, the first thing I wanted was a nice salad that was cruchy and I could chew on.

ETP111 karma

Dr. Hoffman, what do you think of the aerospace related Kickstarter campaigns? Is this a viable way to make advancements?

jhoffma12 karma

Kickstarter campaigns have been remarkably successful for limited budget projects. Many space projects require more funds than can reasonably be expected from kickstart. So it really depends on the magnitude of funding required.

Nsteen1 karma

What are the psychological tests of the astronaut selection process like? What tests are involved? What qualities are being tested?

jhoffma11 karma

Interviews with psychologists are a standard part of the selection process, to root out anyone with a psychosis or serious neurosis.

WaitForItTheMongols1 karma

Hi Professor Hoffman! I was in your 16.00 class a few years back. Have you seen anything in the blimp competition that really impressed you?

jhoffma12 karma

We are now letting students design and build their own balloons, which has led to some interesting results.

Phantom08091 karma

If you could instantly fund and approve one NASA space mission currently in the works or at least being discussed, which one would it be?

jhoffma13 karma

1 - Lunar Resource Prospector, to see if there really is water in craters near the poles of the Moon.

2 - Mars Sample Return

3- LISA (space-based gravitational wave detector)

Phantom08091 karma

What do you think of breakthrough starshot? Is it viable? or is it too far off in the future for it to matter?

jhoffma12 karma

I don't know if it is feasible, but it's a great way to get people thinking out of the box and stretch their imaginations.

EleanorSSmith1 karma

With water being so heavy yet vital to sustain human life, how is it supplied to astronauts during their time up in space?

jhoffma11 karma

Water is, indeed, heavy, and launching it is expensive. That is why recycling water is so important. The Space Station currently recycles over 3/4 of their water, and we are continually trying to improve the recycling percentage.

dxiri1 karma

is there a way a technology professional (think IT, programmer, sysadmin, etc) can go into space?, has there been any technology hands-on work needed on the ISS that requires technicians to go up there and fix stuff?

jhoffma12 karma

Computers can be reprogrammed from the ground, so I'm afraid that's where most IT experts will be for awhile at least. Sorry.

guptanitesh1 karma

Do you think there is a future for Aerospace engineers, specifically propulsion engineers?

jhoffma11 karma

Aerospace is a vibrant field, with lots of new technologies being developed. We desperately need better propulsion, but currently nobody seems to know how to do this.

space_gardener1 karma

Can we build a space ship that can travel between stars. It is so lonely to celebrate just reaching edge of solar system. I know it is not a small feat, but we really need to travel more far right?

jhoffma12 karma

It depends a lot on how long a view you take. In the longest view, our Sun will someday die. If humanity wants to survive, we need by that time to be able to travel to other inhabited planets. In the nearer term, I think that life is so precious that bringing it to another planet, like Mars, would be a positive ethical good (assuming that Mars doesn't already have life, in which case we need to preserve it.)