cryogen

Spiegel's source is an astronomer who's part of that group (or at least has inside information).

That's not really fair; JWST has an enormous wavelength range, even more logarithmic range than Hubble. JWST spans 600 nm - 28.5 μm between two cameras (NIRCam and MIRI), while Hubble's cameras span from 115 nm to 1.7 μm, up to 2.4 μm when NICMOS was still operating. https://directory.eoportal.org/web/eoportal/satellite-missions/j/jwst

It's probably invisible, actually. Hydrogen gas has very little emissivity; it's transparent and doesn't glow when heated. Check out photos of the RS-25 engine (shuttle launches, or SLS engine tests); they're almost totally invisible, except for a faint blue glow. Even that glow is probably caused by steam (this person suggests chemiluminescence from radical recombination, I assume OH radicals), and wouldn't show up in a pure-hydrogen exhaust stream. RS-68 engines, by contrast, have an orange-pink glow, despite using the identical LH2/LOX fuel as RS-25. The difference is that RS-68 is an ablatively-cooled engine, which means the engine nozzle liner is slowly vaporized to provide evaporative cooling. It's this ablated organic material in the exhaust stream that makes it colorful. I suspect the pink color visible in NTR ground tests is also caused by something ablating; I don't know. If a flight NTR engine involved something ablating, then that could introduce some color; maybe it'd look like RS-68. I think it could be something ablating into the exhaust stream, maybe the protective of the nuclear fuel. That eroded pretty fat in the NERVA tests, but I can't find confirmation they're responsible for the color. Yes, the KIWI B1A test was aborted early because of a large hydrogen fire. According to p. 29-30 of http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19920005899.pdf That's the rule for emissive blackbodies -- it doesn't work here, since a hydrogen gas is very far from a blackbody (in fact hardly emits anything). You can see in photos that RS-25 engine exhaust barely emits any light. You get closer to a blackbody with massive, solid particles, like the alumina dust in SRB exhaust that makes it glow bright white. Exactly, an NTR SSTO would be very difficult (see Kirk Sorensen's blogpost), and you don't want an NTR first stage that returns to Earth. TIMBERWIND was a NTR 2nd stage with impressive payload improvements -- but the economics would probably be horrible. https://en.wikipedia.org/wiki/Project_Timberwind Exactly -- if anything, they're limited to being somewhat cooler. Their enormous Isp advantages doesn't come from higher exhaust temperature, but from the exhaust having much lower molecular mass.

I think you're thinking of the upper stage engines. NASA planned on using (an update of) the J-2 engine, the one from the 2nd and 3rd stages of Saturn V, as the upper stage engine for SLS. (And prior that, Ares I and Ares V). They ended up dropping it in favor of RL10. https://en.wikipedia.org/wiki/J-2X

You got it. The reason Orion exists is there was a project to go the moon and so they designed this capsule, an analogue to the Apollo CM. Around 2010, the moon project was cancelled, but there was a political rift, some politicians tenaciously held their grip on Orion's budget. So we keep building it. There's no reason any more, only rationalizations and inertia.

Here's a useful article about super-sized EELV derivatives: https://www.cbo.gov/sites/default/files/109th-congress-2005-2006/reports/10-09-spacelaunch.pdf I don't think there's much market for heavy EELV's (at least at ULA pricing), given that Delta IV Heavy launched only 9 times in the past 12 years. And none of them were commercial launches. As for USAF, they can't buy many more Atlas V's because of the RD-180 embargo.

I think the answers in this thread about MLI are only partly right (as is the Wikipedia page on MLI). From some research, it looks like multi-layer insulation (MLI) can use either aluminized or goldized Kapton; while the aluminized version has a deceptively "gold-color" appearance, there's a different type that uses actual gold (Au), the element, vacuum-deposited on Kapton film. This makes sense, since gold has pretty unique radiative properties; it has significantly higher α/ε ratio than aluminum -- it's a "warmer" material in direct sunlight. Here's one source, a NASA technical document about MLI: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19990047691.pdf Here's a second source, an article by a company that manufactures MLI films (note it's one of the vendors listed in the previous table): http://www.sheldahl.com/documents/Thermal Control Overview.pdf According to the first pdf (NASA), the MLI insulation on the Solar Maximum Mission in the 1980's was goldized Kapton. Here's a picture of it, showing a very unique color, darker and more reddish than other spacecraft (unless there's something wrong with the color camera?) http://solarscience.msfc.nasa.gov/SMM.shtml A couple more photos of goldized Kapton MLI. The source pdf is http://esmat.esa.int/esa_str-241.pdf For comparison, here's Cassini's MLI insulation, which looks quite different, rather yellow-ish. According to this source, these are aluminized films, including Kapton, Mylar, and Dacron; http://www.jpl.nasa.gov/releases/97/csblank.html

That's characteristic energy, C3. It's not a delta-v figure per se; it's equal to v∞2, i.e. the asymptotic limit ("at infinity") of the Earth-relative velocity as you leave the Earth's SOI. Squared. So if you're leaving Earth with a C3 of 130 km2/s2, you're departing with an Earth-relative heliocentric velocity of more than 11 km/s. It has a wikipedia page: https://en.wikipedia.org/wiki/Characteristic_energy It's often used to measure launcher performance (on the x-axis): https://www.nasa.gov/sites/default/files/files/NAC-July2014-Hill-Creech-Final.pdf

Ozone as a rocket oxidizer was studied in depth in the 1950's. In theory you could get 20-30 seconds increase in Isp from it, over plain oxygen. It's thought too unstable to be practical. Here's an excerpt from John D. Clark's Ignition!: An informal history of liquid rocket propellants, which is out of print (and currently sells for $2,904 on Amazon ) (reposting my own comment from an older thread)

Here's the paper (33 pp), http://arxiv.org/abs/1510.06387

Cool! That guy with the blue wire running out of him... Might be that they're running a neutral gas atmosphere in there, and that's his personal air line.Those are "SCAPE suits", used when working with highly toxic rocket fuel (i.e., hydrazine and nitrogen tetroxide). They're at positive pressure for leak safety (just like biohazard suits). The blue hoses are air supplies. So that photo was likely taken when they were fueling the satellite before launch. http://sci.esa.int/rosetta/33116-scape-suit-training-is-given-by-the-csg-safety/ http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110008456.pdf Some more views (click for sources + captions): (Photo credits: ESA/CNES/Arianespace/Optique vidéo du CSG, and P. Baudon)

I recommend J. D. Clark's "Ignition" for a scary history of Cold War-era propellant labs. Some of the craziest fuels researched were Hydrazines / N2O4 (we're still using this... ) Fluorine compounds (liquid F2, ClF3, ClF5, OF2, O2F2...) Ozone (O3) Beryllium (metal, beryllium hydride...) Boranes (B2H6, B5H9...) Mercury (metal, dimethylmercury...)

The problem is that Pluto has little gravity (vesc = 1.2 km/s), so the Oberth effect gives you no help with capturing into orbit. Any realistic trajectory arrives at Pluto with a very high vinf, and all of that has to be cancelled with propulsive delta-v. New Horizons' flyby was at a relative speed of 11 km/s, which would be impossible for chemical propulsion to cancel. If you work out the orbit equations, more realistic speeds would give you ridiculously long flight times, like 30-50 years! What you'd need is high-Isp propulsion to decelerate to Pluto from a high vinf. Since this happens very far from the sun, you need nuclear or radioisotope propulsion. "Kuiper Belt Object Orbiter Using Advanced Radioisotope Power Sources and Electric Propulsion" http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110014485.pdf "PRELIMINARY DESIGN OF AN ADVANCED MISSION TO PLUTO" http://www.esa.int/gsp/ACT/doc/PRO/ACT-RPR-PRO-ISTS2004-Pluto.pdf There's a couple design studies for Pluto/Kuiper orbiters. I'd guess a lander wouldn't be much more difficult, given the low gravity. But there's very little payload mass to work with, so it'd have to be tiny. [TABLE=width: 800] [TR] [TD][/TD] [TD][/TD] [TD][/TD] [/TR] [TR] [TD][/TD] [TD]NASA GRC / JPL[/TD] [TD]ESA[/TD] [/TR] [TR] [TD]mass[/TD] [TD]3,172 kg wet (130 kg science payload)[/TD] [TD]830 kg wet (19.3 kg science payload)[/TD] [/TR] [TR] [TD]launch[/TD] [TD]Delta IV Heavy + Star 63-F, 70 km2/s2[/TD] [TD]Ariane V, 100 km2/s2[/TD] [/TR] [TR] [TD]gravity assists[/TD] [TD]Jupiter[/TD] [TD]Jupiter[/TD] [/TR] [TR] [TD]tof[/TD] [TD]16 years[/TD] [TD]16 years[/TD] [/TR] [TR] [TD]power[/TD] [TD]9x 550 W Stirling generators (4,950 W)[/TD] [TD]4x 300 W GPHS-RTG (1,200 W)[/TD] [/TR] [TR] [TD]fuel[/TD] [TD]54x GPHS (23.4 kg Pu-238; 13,200 W heat)[/TD] [TD]72x GPHS (31.2 kg Pu-238; 17,600 W heat)[/TD] [/TR] [TR] [TD]gridded ion engines[/TD] [TD]1+1 redundant NEXT (Isp = 3,327 s)[/TD] [TD]2+2 redundant QinetiQ T5 (Isp = 4,500 s)[/TD] [/TR] [/TABLE]

The chemical propulsion variants descend from lunar orbit to low altitude, to get exactly the same Oberth boost. They'd be nuts not to. On that note, does anyone have a mirror of that paywalled .pdf on NASASpaceFlight? It's a US government publication, so it should be in the public domain, by statute. We're all missing details here. I wonder if you could you use SEP spirals from LEO to lunar orbit? (It's like a 2:1 to 3:1 mass ratio savings). How critical is the van Allen belt radiation for that, and could you maybe avoid it by spiraling in the polar direction? (I've been curious if you could use this as an upper stage for outer planets probes -- spend 2-3 years prepositioning a storable CH4/LOX stage at EML1, using an SEP spiral, then send up the science package to rendezvous at EML1, dip down to low altitude, and do an interplanetary burn there to a high C3..)

Strontium is problematic because it's difficult to shield. Beta radiation itself doesn't go far but, when it stops, the impact creates secondary x-rays (bremsstrahlung) that are a lot more penetrating. It doesn't help that 90Sr's betas are very energetic -- 2.28 MeV from its daughter 90Y. NASA appears (?) to consider it impractical. There are lots of (heavily-shielded) 90Sr generators, but none in space (as far as Google knows). The US tested a prototype (SNAP-17A) intended for space satellites -- this before solar photovoltaics were practical -- but it didn't fly. I can't find information about how they planned to shield it. ORNL-IIC-36, "Strontium-90 heat sources" (1971) (pdf, 144pp.): http://web.ornl.gov/info/reports/1971/3445605716035.pdf "Draft Environmental Impact Statement for the New Horizons Mission" (2005) (pdf, 195pp.) http://pluto.jhuapl.edu/Mission/Spacecraft/docs/NH_DEIS_Full.pdf (pdf, 39pp.) http://large.stanford.edu/courses/2013/ph241/jiang1/docs/schmidt.pdf ORNL-TM-3382 (pdf, 346pp.) http://web.ornl.gov/info/reports/1971/3445606041903.pdf