Saturday, October 31, 2009

The Future of NASA Manned Space

The Augustine commission has published its report, which I read. I largely agree with what they offered. Where I disagree is minor: it is less important to decide whether to scrap the government's return-to-the-moon “Constellation” program or not, and much more important to address fundamental structural problems with a government agency overseeing way too many sacred-cow programs.

"Constellation" includes a new and more capable space capsule named "Orion", a new lunar lander named "Altair", and a family of rockets to launch them named "Ares". In point of fact, I’d recommend keeping the Ares rockets and the Orion capsule on track as currently planned. But, I’d make that the last conventional rocket launcher program to be developed and operated by NASA itself. We will need some Saturn-class launchers no matter what we decide to do, and the Ares-1 and Ares-5 (plus Spacex’s Falcon-9 equivalent to Ares-1) are “it”. Further, I’d mandate that NASA turn these Ares rockets over to private launch operators soonest. I'd also mandate using Falcon-9 for space station access at the earliest possible date.

The commission is right about this (and my reading of western history agrees): the government’s proper role is exploration, new technology developments, and encouraging industry to go exploit things found by government exploration. NASA really should be focusing on some extremely powerful propulsion technologies to make really high-speed interplanetary travel practical, and on some sort of “outside-the-normal-box” launch system to make Earth orbit access really cheap.

For the high-speed stuff, I’d suggest gas-core (not solid core) nuclear thermal rockets, and the nuclear explosion propulsion drive, as items definitely “do-able” in the near-term. Most current government and industry employees have forgotten the very real experimental efforts made in the 1950’s and 1960’s in precisely those areas.

The solid core technology was actually test-fired under Project Rover many times in Nevada, between about 1959 and 1972. Toward the end of that effort, it achieved 700-1000 sec Isp levels at engine-only thrust/weight ratios near 3 to 10. The gas core experiments never quite got to actual engine test, but both gas-phase reactor criticality and adequate uranium fireball confinement were test-demonstrated by 1969.

Gas core engine design projections (with only regenerative cooling of the engine) were 2000-2500 sec Isp at engine-only thrust/weight far over 30. With a massive heat radiator added to protect the engine at high reaction power, the technogy seemed to be easily capable of 6000-10,000 sec Isp at engine thrust/weight near 0.1 (due to the inclusion of the radiator weight).

The nuclear explosion drive was extensively analyzed under old Project Orion in the 1959-1965 time period, but was never tested with nuclear materials. However, a 1-meter scale model flew just fine using pulsed high-explosive charges to simulate the effect. The best-performing designs on paper were very large vehicles weighing around 10,000 tons, and the truly peculiar advantage of this approach is the larger the vehicle the better. For 10,000-ton sizes, effective-Isp was far in excess of 10,000 sec, and it was challenging to hold vehicle accelerations down to 2 gees.

For the cheap launch stuff, I’d look at parallel-burn rocket-ramjet stuff, using the low-volume ramjet, integral-booster, technologies we developed for missiles in the 1970’s (see LTV's ALVRJ, and Martin-Marietta's ASALM-PTV, both of which flew quite successfully). Most of NASA today, and most current industry employees, never knew we did these things so long ago. I would keep the basic low drag-loss fast-ascent trajectory profile, and provide "ramjet assist" to a basic rocket core, only up to about Mach 6 at around 120,000 feet. This is plain kerosene-air subsonic-combustion ramjet stuff, which we have had operational since the late 1940's. Thus, there is no need for "scramjet technology", which is still not ready for application.

Whatever we do, we cannot scrap the space station early. We need it for research on deep space travel, but we will need to add a medical centrifuge to it to test for how much artificial gravity is “enough”, since that answer sets the size and cost of manned deep space exploration vehicle designs. That question now has no answer, because we only have the possibility of experimenting at 1-gee (down here) and 0-gee (up there), as things stand now. We already know 0-gee does irreparable bone damage after about 400 days’ exposure, based on the Russian experiences. This is critical to going anywhere outside Earth orbit, anytime soon.

The commission is also correct in pointing out that the real destination is Mars, but not necessarily the best first destination. Neither is the moon, in my opinion, except in so far as we can safely develop there the nuclear deep-space engines we need. Unfortunately, we are not yet ready to go to Mars, due to crew survival concerns. The twin bugaboos are lengthy 0-gee exposure (3-5 year round trip missions with bigger chemical rockets than we have ever had), and exposure to lethal solar radiation storms. Very powerful propulsion cuts down the exposure time to both hazards, and allows us to fly with at least some heavy radiation shielding.

Other worthy destinations include the asteroids and comets (aimed at figuring out how best to deflect killer impactors), and the moons of Mars (as a prelude to landings there). The commission did not mention destinations further out, but the moons of Jupiter and Saturn would be very interesting places to visit. The baseline design mission for the original old Project Orion nuclear explosion-driven ship back in 1959 was a 3-year round-trip voyage to Saturn in a 4000-ton spacious vehicle built like a steamship. That propulsion technology appears even today capable of supporting a trip like that as a single stage, fully re-usable vehicle!

The commission was right. We need to thoroughly re-think the purposes and goals of our government manned space program. We are fully capable of leaving the cradle and wading out into the ocean of deep space to explore as we have never done before. Why we have not already done so is both a great mystery, and a terrible disappointment, to me.

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