Oct 05 2009

"I feel the need…the need for speed," insist Manned Mars Mission Planners

Published by at 1:27 am under Wave Guide 7: NASA Programs

Much like Tom Cruise, in the popular 1986 movie “Top Gun” — who insisted, “I feel the need … the need for speed” — current manned Mars mission planners are echoing his famous quote. And the way to do that during the 2015 Maslow Window timeframe (~ 2015 to 2025) is with nukes.

Tom Cruise had the right idea about traveling to Mars in his wildly popular 1986 movie “Top Gun.” Click cruise.jpg.

According to Bill Emrich (Smithsonian’s Air & Space, 9/09; Michael Klesius) of NASA/MSFC in Huntsville, “Missions to Mars will almost certainly require propulsion systems with performance levels exceeding that of today’s best chemical engines.”

The motivations include shorter Earth-Mars travel times (and thus reduced space-related hazards like radiation for crews), reduced vehicle weights in LEO (lower Earth launch costs), and increased mission safety and flexibility by broadening launch windows and reducing the need for aerobraking. Regarding the risks of chemical interplanetary vehicles with aerobraking at Mars, Emrich warns, “I’d love to go to Mars, but not on that ship … You’re going down to just a few thousand feet above the surface. It would be a very scary ride … Very little room for error … You get one crack at it.”

You can get a feel for the potential thrills of interplanetary aerobraking by renting the 1984 movie “2010” (A.C. Clarke’s sequel to 2001) and watching Roy Scheider endure the approach to Jupiter.

Although not baselined in either Wernher von Braun’s initial engineering sketch of Martian expeditions in 1953, or in the currently envisioned Ares infrastructure, a nuclear upper stage was seriously considered as an option for the chemical Saturn V upper stage which launched astronauts to the Moon in 1969. Because of system requirements that greatly exceed those for the Moon, future expeditions to Mars will probably use nuclear propulsion.

In NASA’s first serious engineering study of humans to Mars, the 1960s EMPIRE study — Early Manned Planetary-Interplanetary Roundtrip Expeditions — nuclear propulsion was found to be “most important” for human missions to Mars. For example, according to Krafft Ehricke (in January, 1963), who led the General Dynamics, Astronautics (San Diego) EMPIRE studies, a 1975 manned mission to Mars “is in the realm of realistic technological planning; the most critical technical item is the nuclear engine.” The schedule for nuclear rocket development was included as a “classified” addendum (which is not included in my copy!), as you might expect at the zenith of the Cold War. Ehricke assumed a nuclear engine specific impulse (Isp) near 850 s (double that of the Shuttle Main Engines), with an operational lifetime up to 20 hr, and ready restart capability. General Dynamics’ prelim analysis indicated a total program cost (1965-75) of $ 18.5 B, — which puts it near the Apollo ballpark — of which about $ 2 B ($ 13.5 B in 2007 USD) was for the nuclear engine. Given improved materials technology, better computer simulation capability, and significant experience with nuclear systems, the development cost should be much less today.

In 1987, Stanley Borowsky of NASA Lewis Research Center (now Glenn) reviewed nuclear propulsion technology in the context of manned planetary missions (NASA TM 101354). He concluded that “convenient interplanetary travel will require the development of advanced nuclear propulsion systems…” with high thrust, large power to weight ratios, and high Isp. Nuclear Thermal Rocket (NTR) technology is particularly favored — where a nuclear reactor heats propellant and creates thrust — because it is the only nuclear rocket system that has been built and tested. Project Rover, the first nuclear rocket project, began in 1955 (before NASA existed) at Los Alamos and became part of NASA’s NERVA (Nuclear Engine for Rocket Vehicle Application) program in 1960. Before its cancellation in 1973, NERVA had 20 successful tests in Nevada; its highlights included engine endurance (60 min at 1100 MW), high power operation (5000 MW for Phoebus-2A reactor), and reusability (XE-P system was restarted 24 times). However, time ran out before a flight-rated nuclear engine could be tested.

At the Case for Mars IV Conference in 1990, three EG&G Idaho scientists under contract to the U.S. Department of Energy concluded that “the propulsion system likely to meet all mission requirements (for human exploration of Mars) is the Nuclear Thermal Rocket.” They emphasize the performance advantages of NTR versus chemical systems,

For a transfer of 250 days, the initial mass in Earth orbit (IMEO) for a cryogenic chemical system with an aerobrake is about 325 metric tons and about 1,000 metric tons without it. For the same mission, an NTR with an Isp of 950 seconds (an updated NERVA design) would require about 250 metric tons IMEO without aerobraking. This would be even less with aerobraking.

Although they do not quote a cost estimate, the EG&G scientists estimate that an initial NTR would require 5 – 8 years of development.

As we approach the 2015 Maslow Window, when human spaceflight to Mars is seriously contemplated, current Mars mission planners again feel the need for speed. NASA’s Emrich is studying nuclear systems that could cut the Earth-to-Mars travel times in half relative to chemical propulsion. His project, the Nuclear Thermal Rocket Element Environment Simulator or NTREES at NASA Marshall, will subject potential nuclear rocket components to the extreme temepratures they will have to survive during in-space reactor operations.

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One Response to “"I feel the need…the need for speed," insist Manned Mars Mission Planners”

  1. SYSTEM REQUIREMENTS LAB FOR INTELon 21 Jun 2015 at 11:08 am


    21st Century Waves » “I feel the need…the need for speed,” insist Manned Mars Mission Planners…

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