As we continue to rethink the way forward (with Solar system colonisation and Earth transformation in mind as we exorcise the cheerless ghost of Malthus), the possibilities posed by nuke rockets are well worth pondering:
>>By Jeremy Hsu [Space dot com] March 05, 2010
Future Mars outposts or colonies may seem more distant than ever with NASA’s exploration plans in flux, but the rocket technology that could someday propel a human mission to the red planet in as little as 40 days may already exist.
A company founded by former NASA astronaut Franklin Chang-Diaz has been developing a new rocket engine that draws upon electric power and magnetic fields to channel superheated plasma out the back. That stream of plasma generates steady, efficient thrust that uses low amounts of propellant and builds up speed over time.
“People have known for a long time, even back in the ’50s, that electric propulsion would be needed for serious exploration of Mars,” said Tim Glover, director of development at the Ad Astra Rocket Company.
The rocket technology could drastically cut down the amount of time a spacecraft needs to send astronauts on Mars missions. Instead of half a year, a spacecraft could make the trip in just over a month using the engine and a large enough power source, according to an Ad Astra mission study.
NASA’s recent course change has freed up some funding for new propulsion technologies. And the U.S. space agency has not lost sight of the red planet,NASA administrator Charles Bolden told Congress as he presented a new budget last month.
“While we cannot provide a date certain for the first human visit, with Mars as a key long-term destination we can identify missing capabilities needed for such a mission and use this to help define many of the goals for our emerging technology development,” Bolden said . . . .
Ad Astra’s Variable Specific Impulse Magnetoplasma Rocket(VASIMR) ionizes gases such as xenon or hydrogen to create superheated plasma stream for thrust.
But VASIMR also has the advantage of relying uponelectromagnetic waves to create and energize the plasma, rather than physical electrodes that get worn down due to contact with the superheated plasma. That translates into greater reliability over time and allows for a very dense plasma stream to create more thrust.
VASIMR can also adjust its thrust to speed up or slowdown, and even has an “afterburner” mode that provides a temporary high-speed boost at the cost of efficiency . . . .
A mission trajectory study estimated that a VASIMR-powered spacecraft could reach the red planet within 40 days if it had a 200 megawatt power source. That’s 1,000 times more power than what the current VASIMR prototype will use, although Ad Astra says that VASIMR can scale up to higher power sources.
The real problem rests with current limitations in space power sources. Glover estimates that the Mars mission scenario would need a power source that can produce one kilowatt (kW) of power per kilogram (kg) of mass, or else the spacecraft could never reach the speeds required for a quick trip.
Existing power sources fall woefully short of that ideal. Solar panels have a mass to power ratio of 20 kg/kW. The Pentagon’s DARPA science lab hopes to develop solar panels that can achieve 7 kg/KW, and stretched lens arrays might reach 3 kg/KW, Glover said. That’s good enough for VASIMR to transport cargo around low-Earth orbit and to the moon, but not to fly humans to Mars.
Ad Astra sees nuclear power as the likeliest power source for a VASIMR-powered Mars mission, but the nuclear reactor that could do the job remains just a concept on paper. The U.S. only ever launched one nuclear reactor into space back in 1965, and it achieved just 50 kg/kW.>>
Electro-rockets are an obvious long term issue. In the meanwhile, NASA has moved on Nuke Thermal rockets:
>>Today’s chemical propellant rocket engines may not be the fastest or most efficient way to send a crew to another planet. One idea for the next-generation rocket engine you’d need is to bring back nuclear thermal propulsion (NTP) systems. The technology was studied in the 1950s and 60s, but shelved in the early 70s because of technological challenges, and because there was no clear need for the propulsion system.
Jeff Sheehy, chief engineer of NASA’s Space Technology Mission Directorate, says times have changed. Advances in manufacturing, materials science, and engineering have made it possible to design a better fuel element and nuclear reactor than was possible during the Cold War. What’s more, and what has really been lacking until now, is a reinvigorated “desire to send crews into deep space,” says Sheehy. “I mean the desire has always been there, but the push or the emphasis that NASA has had for the last few years about developing that capability—that has renewed the interest in NTP as an option.”A nuclear thermal propulsion rocket engine would use a small nuclear reactor to generate heat from uranium fuel. That thermal energy would then be transferred to a liquid propellant, probably liquid hydrogen, which expands into a gas and is shot out through a nozzle to produce thrust. “So you get the exhaust moving very fast out the back end,” Sheehy says.
To begin work on a new NTP rocket engine, NASA awarded an $18.8 million contract to BWXT Nuclear Energy in August 2017. BWXT, which has a long history of making nuclear fuel for the U.S. Navy, will design a nuclear reactor that uses low-enriched uranium nuclear fuel in the form of “Cermet” (ceramic metallic) rods. NASA has also partnered with Aerojet Rocketdyne to design an engine that could be mated to the reactor to produce thrust, and NASA will study cryogenic storage options for carrying liquid hydrogen propellant . . . .
A spacecraft using NTP could cut the travel time to Mars by 20 or 25 percent compared to chemical rocket engines, Sheehy says. Alternatively, the higher energy output means a spacecraft with NTP could launch to Mars during a broader launch window than spacecraft with conventional rocket engines. The latter are limited to a 30-day window every 26 months that’s dependent on the orbital positions of Earth and Mars.
Perhaps most importantly, NTP engines would allow astronauts on a mission to Mars to more readily abort and fly back to Earth . . . .
A major advantage of NTP engines is that they can run much longer than chemical rocket engines, such as the Space Shuttle main engines or the Merlin engines on SpaceX Falcon 9 rockets, and still produce significantly more thrust than an electric propulsion system, such as the ion thrusters used on satellites. NTP is a happy medium . . . >>
A hope, and a challenge. END
PS: Pardon format, the new update gives problems with blockquotes.