I disagree with the claim in the Jan. 17 op-ed by O. Glenn Smith that manned spaceflight is inherently very “difficult, dangerous, and expensive” [“Unintended Consequences for NASA,” page 19] as well as with the comment in the Jan. 10 letter that “all can agree” that developing the space shuttle was a “good decision” [“Putting ‘Griffin’s Zombie’ to Rest,” page 18]. The motive behind the program — to develop a reliable, fully reusable launcher to dramatically reduce launch costs — was excellent, but the implementation was a disaster from the word go.
NASA needed to seek assistance from the Air Force only because it fixated on the notion by the mid-1960s that Reusable Launch Vehicles Must Have Wings — the RLVMHW paradigm — and, when the time came, was unable to develop its two-stage vertical takeoff, horizontal landing design with flyback booster within the development cost limit imposed by the White House Office of Management and Budget. The Air Force demanded an orbiter with a very high cross-range requirement (never used) as its price for participation in the program, and it went forward. NASA then compounded the blunder during development with its obsession for Absolute Maximum Performance with Absolute Minimum Mass — the AMPAMM paradigm. The end result was the overly complex, partly expendable, fragile, dangerously unreliable, and hideously expensive vehicle we have now.
NASA tried twice to develop a launch vehicle to replace the shuttle — the National Aero-Space Plane and the X-33 — and fell headlong into the RLVMHW and AMPAMM traps both times. Both failed largely because they were single-stage, horizontal-landing designs that had very aggressive dry-mass requirements (and are still well beyond the state of the art). They were selected simply because they were the most difficult ways to build a launch vehicle that NASA could imagine and promised to “justify” a great deal of technology development work for NASA research centers. As Robert Zubrin has pointed out, that is the exact opposite of the proper way to do engineering.
We have had the technology to develop reliable, fully reusable, two-stage launch vehicles for over 40 years, and could have developed a two-stage, vertical takeoff and landing (VTOL) design, with a lift capacity of 40 to 50 tons, for about what we spent on the shuttle. Had we done so, we very likely would have bases on the Moon and Mars right now, but I have found no evidence that NASA has ever even considered such a concept.
A reusable launch vehicle of that size can support manned lunar and Mars exploration with the addition of a propellant depot in low Earth orbit (LEO). The orbiter would arrive at the depot with its attached lunar or Mars payload, refuel, then do the trans-lunar- or trans-Mars-injection burn itself, eliminating the need for an Expendable, Super Heavy Lift Launch Vehicle — the ESHLLV paradigm. The orbiter would dock nose-to-nose with the depot tank set, swing arms would attach the propellant lines, then the entire assembly would be rotated about its common center line to settle the propellants in their tanks, and propellants would be transferred with differential gas pressure — no zero-gravity propellant acquisition devices required. The depot would have previously been filled with three or four tanker flights of the same launch vehicle.
Note that a vehicle that takes off and lands vertically can land on the Moon or Mars, refuel with propellants produced from indigenous resources, then fly directly back to LEO with aerobraking, thus eliminating the need for a separate aerobrake for Mars landing, and separate landing and Earth return stages. Those who shrink in horror at the thought of landing an aerobrake on the Moon should realize that minimum mass does not equal minimum cost.
Congress recently directed NASA to develop a shuttle-derived heavy-lift vehicle with a payload capacity to LEO of 70 to 100 tons, and I do see considerable utility in such a vehicle, especially if the propulsion and avionics module were made recoverable for reuse. That would greatly improve the economics of the vehicle, as would salvaging the external tanks in orbit and converting them to other uses, such as hotels, laboratories and tanks for a propellant depot. That would make the vehicle essentially fully reusable.
An early application could be a low-gravity research facility. Two external tanks would be outfitted in orbit, docked to opposite radial ports of a modified international space station-type node, then rotated about the node axis to create Mars gravity at the bottom of the liquid hydrogen tanks. A simulated habitation module with actual life-support hardware would be placed at the bottom of one tank to test the ability of humans to function long-term in Mars gravity, and a propellant production plant, plus other surface hardware, would be placed at the bottom of the other tank to qualify them for operation in a simulated Mars surface environment.
The heavy-lift vehicle should be explicitly designed to support Zubrin’s Mars Direct scenario, as outlined in his series of commentaries in Space News in 2005 [“How To Build a Lunar Base, Part 1: The Launch Issue,” Feb. 21, page 19; “Part 2: The Mission Plan,” Feb. 28, page 19; and “With Evolution to Mars,” March 7, page 19]. We could be back on the Moon “before this decade is out,” then on to Mars shortly thereafter. As a near-term follow-on, the orbiter stage of the two-stage VTOL reusable launch vehicle could be derived from the upper stage of the lunar/Mars version of the heavy-lift vehicle, with the addition of an aerobrake and landing gear. The booster stage, for example, could be constructed from a cluster of seven Falcon 9 first-stage derivatives.
The reusable launch vehicle would have many other uses besides manned lunar and planetary exploration, thus immunizing those programs from cancellation by shutting down the booster production line, as happened with Apollo. (NASA has failed to learn the lessons of Apollo and has based its proposals in response to President George H.W. Bush’s Space Exploration Initiative and President George W. Bush’s Vision for Space Exploration on the ESHLLV paradigm.) In particular, the reusable launch vehicle could support a robust tourism industry, carrying some 50 passengers to LEO per flight for less than $1 million per ticket. Somewhat later, once we have at least a liquid oxygen production plant on the Moon, it could carry tourists to the Moon for about $5 million per ticket round-trip.