Thomas Stafford: Penmanship in Boxing Gloves
Planning for Mars, The Stafford Way
In the early 1990′s, former astronaut Thomas Stafford was asked to come up with a plan for human missions to the Moon and Mars. In his most recent testimony to the Presidential Commission on the Moon, Mars and Beyond, Stafford revisited that reference design adding his unique perspective. The informal commentary provided a fascinating exchange on what to do and what not to do in mission planning.
I thought it would be interesting to go back just briefly in history to set the parameters. On July 20, 1989, President Bush said, on the 20th anniversary of the first lunar landing, that we ought to set our sights for space exploration for the 21st century this time to return to the Moon to stay and then go on to Mars, by 2019. He then reactivated the space council, with Vice President Quayle as the chairman. The Space Council then asked for a 90-day study of NASA and how they would carry out this vision of returning to the Moon and going on to Mars when this was completed. We came up with four different architectures, ten recommendations, and then the supporting technologies that would take us forward.
We have not been in deep space with humans since 1972. We then envisioned two exploration missions out to Mars. One’s a short duration mission of 60 days, and the other one would go up to 500 days, in the second mission and that would take us to the year 2019.
|James Cameron Mars Design Reference Mission, the wheeled surface transport.|
Credit: J. Cameron
The way the Apollo Program was started, then NASA Adminstrator, Mr. Webb, told the Vice President [Lyndon Johnson] after one day’s deliberation that they could go to the Moon and back in this decade, for $20 billion. And the final cost was $22.4 billion, starting from scratch.
If you look up on the wrap-up on NASA back in the early 1960′s. That was building the infrastructure, building the Johnson and Marshall Space Centers. And the Cape was strictly palmettos, rattlesnakes, and palm trees. In 6 years, that was built to the Vehicle Assembly Building (VAB), and we launched the first Saturn flag. And most of it was done with a slide rule too.
The Saturn V and Apollo were probably the simplest interface, like a meat cleaver and in the two spacecraft, just the thrust chamber pressures from the stages and tank pressures, lit up with I think two wires in case we had to take over and fly by hand the Saturn V, which we could do. That was it. It was the cleanest interface.
|James Cameron Mars Design Reference Mission, the Earth to Mars nuclear transport.|
Credit: J. Cameron
[Relating to today's recommendations to the moon and Mars, one should] push the state of the art when required, very important. And be sure the outlines and technology we push have acceptable risks. Next one, optimum use of man-in-the-loop technology, don’t burden a man where a robot or machinery can do better. In aviation we see it, the 727 started out, and three people in the 727? And now we are down to 777, with 2 people in the cockpit flying very safe. And that was a big debate if you will remember back in the 1980′s, and also again on Apollo, the original one, the computer program, it was unbelievable, we wore out our fingers. Pete Conrad and I helped to rewrite the program after the tragic fire and the stand down for a period of time. So there’s a lot of things that computers and machines can do, and let them do it and let the man be optimized in what they can do.
Limit development time to no more than 10 years and actually the longer it takes, the cost goes up. Redundant and primary systems versus a big reliance on onboard inside maintenance. The Space Station has some of that, but out to the Moon it will be difficult, and Mars it will be tough to do anything on that one.
Ten years is the outer limit, and probably the long pole in that tent would be the nuclear part on that. But, you know, the basic part to get started for the initial operational capability, because you do have some elements that have some heavy lift with the Space Shuttle, you modify it and work from that.
Allowing software to run unchecked, becomes a constraint rather than support element. I think if you look at Apollo, one of the long poles in the tent was the software. Used to have black Saturdays all the time and we did not have that many words in the computer. And the same with the Space Shuttle, the software was one of the main constraints on getting that airborne, and also the software on the Space Station, unbelievable from the original lines of code to where it’s set up now.
The last one, when you are wrong, say you’re wrong. That was a picture I shot on Apollo 10. We disproved the British Flat Earth Society. The Earth is round.
Well, the architectures we came up with were, the first one was, we take the minimum resources there, and that’s the Mars exploration. And what this was, it was an exploration to go back to the Moon and then do their science and exploration, but also do the best simulation we could of going on to Mars.
Why should we go back to the Moon? That question was asked among our groups. Why should we go to the Moon, we’ve been there. But then as we continue into these months of deliberation, it was determined that the Moon made an ideal testing place. We can also do science there. You would take the type of habitat, the rovers, the spacecraft that you would have on Mars, you can test those on the Moon, it’s only 3 days away. And it’s operated in deep space.
[To get to] Mars, we can have a window every 26 months, and the amount of energy it takes repeats itself in the sinusoid every 15 years. And 2003 happens to be the minimum energy year, and we saw these two rovers up there now, transited out to Mars in only 6 months, sometimes it takes well over a year to get out there.
And so from the time we started the Synthesis Group we saw that 2018 will be an era of minimum energy and we would start down on that curve, starting with 2014 and going out there.
|Lunar Clementine mission shows the South Pole of the Moon. The permanently shadowed region center shows evidence of meteor cratering and ice never exposed to direct sunlight.|
Credit: NASA/DOD Clementine
But the exploratory part first would be done there on the Moon, and you would simulate what you were going to do on Mars and you could simulate the transit time. You go down to the Moon and work back, and you’d have a large safety factor because Mars with 38 percent of the gravity of the Earth and the Moon, 16 percent of the gravity, you have a good safety factor to work with and you would simulate then what you would do on Mars, on the Moon to take care of that.
The next one, science emphasis, this requires far more resources. You would look at areas like a large baseline interferometer telescopes looking into deep space where theoretically you could see planets around stars, you would then have also more on Mars. This is a far more ambitious type of architecture.
The next one, the Moon to stay, this emphasized human presence this would be a build-up, we’d have initial operational capability and then we’d have follow-on operational capability and from that we’d then also have the Mars exploration similar to architecture one.
And then the space resource utilization, that was what we called the wild card, far more resources required, but also could present a far better return back here to the Earth. And again, at the end of the one-year study, it’s here, America at the threshold — there were 80-some boxes of books presented to NASA behind that, but that’s what we had.
[The first option is most like the current one]. It was just to the Moon to do some minimum exploration and to verify, you know, that the equipment you had would go on to Mars… The Gemini and Apollo program built one on top of the other and this is built in the same way and here we had what came out. You see the explorations in sciences, one of them is the human presence. And then space resource development. So this was the first one, and then we had the second one. The Moon to stay was the third one I mentioned, and the fourth was the space resource development, but they all had that common theme of exploration and science, of human presence and space resource and development. So you could take various parts of them.
The next one that came in was the space exploration initiative’s requirements into the heavy lift program. This is somewhat modified as you know, because when the administration changed in the end of 1992, the space exploration initiative was pretty much zeroed out. The DoD continued on with expendable launch vehicle, with the evolved expendable launch vehicle, but they have capabilities that are somewhat limited as far as I think 40,000 to 50,000 pounds. And to do this and go back to the Moon and on to Mars, you need far more than that. We estimated in our recommendations that we have approximately 150 to 250 metric tons to low Earth orbit.
The one thing that has changed too is miniaturization has continued on with respect to electronics. The pay loads and the landing parts and material developments on the lunar surface of Mars has gotten slightly less, so therefore, you could do it with less lift into low Earth orbit. As we continued on, we used Jet Propulsion Laboratory running trajectories and simulations.
|Mars robotics pave the road to the Red Planet|
Image Credit: JPL
We said that to go back to the Moon, and for chemical propulsion was adequate as we did in Apollo. But to go beyond that, to Mars, like, I’m going from memory now, but to go from low Earth orbit to lunar orbit and back to landing, is around 5 kilometers a second. To go from low Earth orbit to Mars orbit, depending where you are, the 15-year sinusoid varies from about 8 kilometers per second to 24 kilometers per second, so that is a big amount of delta. You have to add to get out there.
It became obvious the nuclear thermal rocket technology development, we determined, was the only real practical way to go to Mars. For the Moon, chemical propulsion was perfectly acceptable as we did it. But to go to Mars and the amount of energy required, you basically would like for humans to have a nuclear thermal rocket. We had that capability developed in the United States in the late 1960′s and the early 1970′s with the NERVA program, it showed a specific impulse of 845 seconds, it was run continuously on one occasion for over an hour and did about 28 automatic start-ups and shut downs, but there was not a mission for it, so it was canceled. It was the opinion of the group after all the study that the nuclear thermal rocket technology needed to be developed for the mission to Mars.
It can be perfectly safe in the way that you have all the safety factors with — nuclear physics that in case for some reason it happens it doesn’t go on, it’s not going to give you any radio activity anywhere. The only time you have radio activity is when you pull the control rods and by then, you are in Earth’s orbit headed out. So it’s not going to affect anything here on Earth.
The next one, space nuclear power technology based on [Space Exploration Initiative's] SEI requirements – to do adequate work for in set to processing, for adequate work on both the Moon and particularly Mars, you needed space-based electrical nuclear power. This could also, we determined later on, be used for low level propulsion – the trajectory – to speed you up using ion propulsion or — magnetoplasma dynamics. I also want to commend Sean O’Keefe, within the first 2 to 3 months of his administration, he put forth the NASA nuclear initiatives to start developing this type of technology.
The number one priority is crew safety. In Apollo, it was 99.999 percent. Mission success was 0.90. And Apollo 13 was not a success in terms of finishing the mission. We were 0.99 out there as far as crew safety. Again, you know, it’s not risk free. This has been well demonstrated.
|Dry ice and frost on Mars. Credit:Viking/JPL|
Focused life science experiments – the biggest risk going out there, you know, if you assume that you’ve got your systems down where the systems failure would be very low is going to be radiation. I think this question was asked about risk, and we understand that fairly well. You have galactic cosmic radiation, very difficult to shield against however, it’s not that hard. We understand that the main thing is the solar radiation, and it goes in a cycle. But also you can have a series of unpredicted flares.
If you go back in history, we were good on Apollo, but we were also lucky. After Apollo 8, a large flare occurred. And then in the last year we did the last two Apollo missions, Apollo 16 was in April of 1972, Apollo 17, the last one was in December. On August of 1972, one of the largest solar flares ever recorder erupted instantly even though we are trying to track and predict it. And had those two crewmen been on the surface, they would have received possibly up to a lethal dose of radiation. They might have made it back to the lunar module and to orbit, but they would have a fairly short life span. It is a risk, but there are ways to shield against it, and we will discuss that in just a few minutes.
But we do understand about the risk to humans. And in focused life science experiments. The human body needs about 6 1/2 pounds of water a day, — 2.5 pounds of oxygen and approximately 1.5 pounds of solid food, and most Americans get more than that.
At the Johnson Space Center, they did run closed life support to recycle oxygen and water, and for people up to 90 days, it worked very good, practically no loss of water or oxygen. This is one of the criteria to go out to the Moon and particularly to Mars. If you have to carry all that water and oxygen, it’s very difficult to do that.
They did a 90-day, four-person closed-loop study, and it was finished [at Johnson Space Center] in 1997. They completely closed the water loop and the oxygen loop and amount of water and oxygen loss was very minimal. So this type of technology needs to be put on board and demonstrated, and taken to the Moon and Mars, it drastically reduces your gross take-off weight.
The heavy lift program, the — we’ve discussed that before. I probably discussed a lot of those just going through the iterative efforts and, today the Shuttle modified, I think it can take between 60 and 80 metric tons. It would take several of those together with a series of — even though you want to keep the basic joining in space to a minimum, but it’s advanced a lot in the past 12 years and it’s amazing. Today with CAD, with the Internet, from Russia, Japan, from the European countries, we have put together a precise interface, and I’ve even been surprised how well the Space Station has gone together and fitted real well. It’s probably not as much as of a basic problem as we outlined at that time, so there’s been some improvement.
The nuclear thermal rocket we discussed. I think very definitely that this needs to be done, and we’ve got — it will take a period of time, and this to me is the long pole in the tent going to Mars is that nuclear thermal rocket.
The space nuclear power technology of — that would go up to five megawatts, we estimated. And the minimum we would start with would be 100 kilowatts. And the Prometheus Program at NASA has now started up, but the program at which it’s under – the Jupiter Icy Moon Orbit program – JIMO I’m concerned that this needs to really be focused and have adequate attention from management to get this nuclear development completed. Had a previous one on space – from NASA, as far as space nuclear power, and it was not too much of a success. I think it was the SP-100.
|Prototype of nuclear-fueled JIMO spacecraft, with its heavily finned shape|
Image Credit: NASA/ JPL
These life science experiments — this is ongoing also, and you need to have suits on, and lightweight pressure suits. Because if any of you have ever worn a pressure suit and not fitted right, it’s like doing a penmanship contest using boxing gloves. It’s very difficult.
When we started training underwater after my second mission, Gemini astronaut Gene [Cernan] lost 10 1/2 pounds in 2 hours outside and we had a tough time getting him back in. There needs to be a lot of development in pressure suits. Lighter weight, far more flexible, particularly in the gloves and dexterity. This was ongoing when it was canceled. There needs to be effort there, there has been lots of progress, but for a fairly small expenditure of money, a further improvement in those suits can be done.
So you would like to have the same dexterity you have here at sea level, but I think it’s probably going to be impossible, but you can get close to it. And most of those suits, we had 3.5 pounds per square inch pressure in Gemini, and Apollo about 4.1, and today on the Space Station about 4.3 pounds per square inch.
The Russians have a unique system, and if you get into trouble, you can lower the pressure. We can’t. That’s how Leonov saved his life and got back on, it was risky, but you can lower the pressure. They have had the same problem with their pressure suits, but with adequate development, we can have some very effective suits. If you are going to live on the Moon for a long period of time or Mars, you will have to have the pressure suit that’s very good and not tax so much of your strength.
|Earth in moon perspective|
Image Credit: NASA/GSFC Simulation
Let’s go – I have the technology priorities. There. And again we have — this was the order of priorities of the supporting technologies for this, and we have talked about — but that was a priority. If you don’t have heavy lift, it will be impossible to do this, nuclear thermal propulsion, extra power. Cryogenic transfer and long-term storage particularly on the Mars mission with liquid hydrogen. Even on the best installation, you lost close to 1 percent a day on boil-off. The installation and technology is better, but that’s a problem. Russia has had automated docking from the Soyuz to the Mir and now the Space Station. It’s an engineering problem, 50 to 100 tons of docking. It can be done with the right torque to inertia ratios. And that’s something that needs to be completed.
The radiation effects and the shielding. We came up with adequate shielding around 16 grams per centimeter squared of water. And the best thing to negate the radiation coming in is really the hydrogen atom, and from this, the best thing is really water. And with that, that would stop all the solar flare and any secondary radiation that would come forward.
Telerobotics, very important point when you are on the Moon or Mars, that you could have a series of efforts there between both the human and the robotic-type spacecraft controlled by the flight crews. The closed life support systems, that was mentioned briefly, you have to close the loop for oxygen and for water. Now, we said it was not feasible to try to close the loop for food. Just in either the Moon or Mars missions that we looked at. And that would take us way out through past 2020.
If you are really going to be there on that third architecture for a long time, the Moon to stay for a long time, you would look at possibly recycling the food, but basically it did not make sense as far as the other missions. You could take that with you. You could afford the amount of payload in the low Earth orbit.
|James Cameron Mars Design Reference Mission, liftoff from Mars on the round-trip.|
Credit: J. Cameron
Transhab came out of Lawrence Livermore Lab, an inflatable structure with a reentry vehicle. This is a habitation quarter, inflatable, very light weight. Turns out the way it was built, you see the gray areas at the top and bottom, this type of structure, it was demonstrated, it really has more micrometeorite protection than the Space Station does that’s flying right now. And furthermore with water tanks around, it adequately shields you from radiation, from solar radiation and a little galactic cosmic radiation.
[The trip to Mars is] something like 240 days if you do chemical and 100 days or less if you do nuclear thermal propulsion. With just a slight increase in nuclear thermal, you can cut the transit time down from 240 days to 130. And if you have any electrical power propulsion, therefore ion propulsion, you can cut it down to about 60 days. Now, this drastically reduces your gross lift-off weight and directly relates to cost and staging and everything else.