IAMA 022015 TK JHb TK A1 Q2 Book

http://www.reddit.com/r/IAmA/comments/2wh6fx/hi_everyone_im_thomas_knoll_and_25_years_ago_this/coqunte?context=3

[–]Universu[??] 1 point 2 hours ago
What is your favorite book?

[–]Thomas_Knoll[F,S] 3 points 2 hours ago
To be honest, I don’t read any Photoshop book. Is this a book in general?
My favorite book is “Surely you’re joking, Mr. Feynman!” by Ralph Leighton and Richard Feynman.

[–]Universu[??] 1 point an hour ago
Yes:) a book in general, I guess Lemon Cream Tea is quite good just like Photoshop:)

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IAMA 022015 TK JHi JH Q1 ACUITY

http://www.reddit.com/r/space/comments/2wg2ly/i_am_jeff_hoffman_mit_professor_of_aerospace/coqy3ve?context=3

[–]PatientOne1117 6 points 7 hours ago
Dr Hoffman is it true that landing on Mars is a huge challenge because we only have solved landing on
Earth and the moon? Earth gives us thick atmosphere to help descent and the moon gives low gravity.
Mars gives neither.

[–]JeffHoffman[F,S] 13 points 6 hours ago
This is a good introduction into the many reasons why “Mars is hard”. The heating phase of Earth
reentry takes place at around 250,000 feet (~80 km). Mars atmospheric pressure at the surface is
about like Earth pressure at 100,000 feet, so the reentry heating for Mars entry has to be dealt with
by heat shields, just like for Earth. On the Moon, there is no atmosphere, so all braking has to be
propulsive, using rockets. Luckily, as you point out, the Moon’s gravity is only 1/6 the Earth’s, so
this can be done without too huge a rocket engine. On the Earth, once you have slowed down, you can
land with a parachute or with wings (e.g. Shuttle). The atmosphere on Mars is too thin for this, so
you need more propulsive braking, possibly followed by airbags for a small payload.
A serious problem is that Mars is far away, and getting there takes a long time, so astronauts are
exposed to a lot of radiation. This is one of the most serious problems.
Another problem is the cost of getting anything to the surface of Mars. To land one ton on the
surface of Mars, you need to put between ten and fifteen tons of propellant in Earth orbit. This is
why learning to use local Martian resources could make a huge difference in reducing cost.
I am currently working on an experiment called MOXIE, which will go to Mars on the Mars2020 mission.
For the first time, it will demonstrate the production of oxygen using Martian resources
(electrolyzing CO2 in the Mars atmosphere to make oxygen).
I think we could go to Mars right now using brute force techniques like we did with Apollo, but we
don’t have an Apollo budget. Therefore, NASA is trying to support the development of technologies
that will reduce the cost and risk of exploring Mars, such as the MOXIE experiment I just mentioned.

[–]Universu[??] 1 point 12 minutes ago
May MOXIE pave the way for the fuel of Raptor or BE4 on Mars:) Would you name Mars2020 “Acuity”?

Jeff Hoffman’s @reddit_AMA is live! Ask him anything: http://ow.ly/JkJ4n @reddit @MIT @NASA #SPACE

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