More on the future of NASA

[unixronin]

smandal pointed me at this excellent analysis on Ars Technica.

Regarding the initial news reports, I don't know that it's so much that the reports were intentionally slanted, so much as that they were written from the viewpoint of the general news media's typical appalling ignorance about science: they don't even know enough about the subject to know what parts are actually important.  They don't understand why in-space refuelling matters.  Heavy lift capability is funny science words to them.  They don't understand the technical shortcomings of ARES.  But "The entire Constellation program is cancelled"?  THAT, they understand.  So that's what they reported.

Comments

[montieth.livejournal.com]

I'm still confused. They're selling/giving away motors that work now. They're scrapping the development of the aero spike engines that are looking to give FAR more thrust. What are they going to use for the heavy lift? Wishes? Unicorn farts?


7 Billion in development of engines isn't wasted money. It's science and engineering that you can continue to use. If we're pulling parts back from the Saturn V program then money spent there is STILL paying dividends.

[unixronin.livejournal.com]

I'm a little puzzled myself why they're giving away the SSMEs. The SSME is a damned good engine. I can't confess to any sadness at the Morton-Thiokol segmented solids being ditched; they've never been able to lick the vibration problems with them, they're not throttleable, and they burn dirty as hell.

I don't know if anything's being pulled still from Saturn. The Saturn V's F1 engine is still the most powerful single rocket motor ever built, if memory serves, and is — again, if memory serves — another engine which has never failed in service. But when they were developing the F1, they had terrible combustion instability problems, and they ended up just more-or-less-randomly drilling holes in the diffuser plate until it worked, then copying that pattern of holes. There was never a theory behind why it worked; it just did, and that was good enough.

I don't know why the aerospikes are being cancelled. It certainly sounds like a very promising technology.

[montieth.livejournal.com]

What's crazy is the Ares V heavy engines, generate 1,000,000 lbs of thrust. Apparently they needed pumps that would work for these. Nothing they had worked. Apparently someone realized the F-1 Pumps DID flow this quantity of LOX and HOX. So they went through the junkyards that this gear was scrapped in, and bought back the pumps.

Why NASA doesn't find a warehouse somewhere and Mothball all this hardware, I don't know. It's a damned waste.

[lebo-superman.livejournal.com]

As I see it, the ideal scene would be a reusable vehicle that could attain escape velocity only with it's own engines, could operate in space, would be maneuverable, have variable (user-controlled) speed, could be refueled in space, and has a heavy-lift capacity.

Well, we already had all but the heavy-lift capacity with the SR-71! Am I right? Why not see if that technology can be adapted to a heavy-lift vehicle? Perhaps all that would be needed would be two more of those high-thrust engines to off-set the addition of the cargo bay.

[unixronin.livejournal.com]

Um, no, you're not. The SR71 cannot operate in space and is roughly 22,000mph short of being able to attain escape velocity with its own engines. The SR71 is capable of slightly north of 2,200mph (Mach 3.2+) and it's officially-admitted service ceiling is 85,000 feet. Earth escape velocity is approximately 11km/s, which is roughly 24,600mph. To attain low earth orbit requires around 8km/s (roughly 18,000mph). Even if the SR71's turbojets were capable of powering it to such speeds (which they're not), it would burn up in moments at such speeds in atmosphere dense enough for its engines to operate. Ramjets can reach speeds as high as about Mach 5.5, but have a minimum speed approaching Mach 0.5 and don't actually produce useful power until close to Mach 1. Beyond Mach 5.5, you need scramjets, but scramjets have a minimum functional airspeed of about Mach 4.5. (You see where this is going, right?)

Current projections based on the X-30 vehicle seem to indicate that scramjets run out of steam somewhere around Mach 17 because above that speed you simply can't supply them with fuel fast enough to continue increasing thrust. LEO requires about Mach 24. So an air-breathing vehicle such as a modified SR71 would need turbojets to get it up to speed to light off the ramjets around Mach 1, then the ramjets could get it up to about Mach 5, fast enough to light off the scramjets which could take it to maybe Mach 17, and then you'd STILL need a rocket stage to reach orbit. So you'd need four different propulsion systems, and at least two different fuel systems (the most likely fuel sharable between scramjets and rockets is cryogenic liquid hydrogen, but it's too bulky to use for all four) on one vehicle. It would be so inefficient that if it could reach orbit at all, it would have no useful payload.

A better approach would be to use an airbreathing launch vehicle that could carry a hybrid-cycle rocket/scramjet orbiter up to around Mach 2 at around 70,000 feet, at which point the orbiter would separate, accelerate on rocket power to the Mach 4.5-5 range, light off its scramjets, shut down the rockets and accelerate to Mach 17 on scramjets, then switch to rockets again for the final climb to orbit. This would allow a 100% reusable two-stage-to-orbit vehicle; it ought to be able to carry a useful payload to orbit, but it probably wouldn't be a large payload, and certainly wouldn't be in the heavy-lift class. It would be eminently practical for carrying passengers or ISS crew replacement.

The biggest problem with heavy lift is mass ratio. To overcome the mass ratio problem, there's really only one solution: you need a combination of high thrust with very high specific impulse. The Shuttle's SSMEs produce less thrust than a Saturn V's F-1 engines (roughly half a million pounds per engine, vs. the F-1's 1.5 million pounds) but at almost twice the specific impulse (roughly 450 seconds vs. 263 for the F-1). So an SSME produces a third of an F-1's thrust, but uses only about a sixth as much fuel to do it. A new Saturn VI booster, assuming F-1 class engines as efficient as the SSME, might be able to lift 250,000lb to orbit, but require less than half as much fuel to do it (because not only does it need half the fuel per pound of thrust to start with, but it only needs to lift half as much fuel off the pad, which means less total thrust is needed, further reducing fuel consumption). The Saturn 5 has a mass ratio of 23.1, and a payload fraction of 0.957; it takes 23 times its own launch weight in fuel to reach orbit, and 4.3% of its weight reaches orbit. The Shuttle is considerably better, requiring 15.4 times its weight in fuel to put 6.5% of its launch weight into orbit. (ESA's Ariane V is truly awful, with a mass ratio of 39.9 and puts only 2.5% of its launch weight into orbit.)

For a true reusable heavy-lift vehicle, we need much better mass ratios, and that means much higher specific impulse. Variants of the never-completed NERVA nuclear rocket engine have theoretical specific impulses in the range from 800 (for NERVA 1) to 925 (for NERVA/NTR); a reusable vehicle using a NERVA engine might achieve a mass ratio as low as 5 to 6, and a payload fraction perhaps as high as 15%.

[lebo-superman.livejournal.com]

Alright, I can work with that. I guess my info on the SR-71 lacked certain specifics. I checked the Wiki on it, and your data matches theirs.

But I thought I remembered reading a report on the final journey of the SR-71 that is now in the Smithsonian - that it made the trip from near LA to DC in roughly an hour. Mapquest calls that a 2674.44 mile trip. True, it's not "as the Blackbird flies" - but passing between radar "gates" at St. Louis and Cincinnati (as reported in the Wiki article) isn't a straight-line flight either. It looks to me like their 67 minute flight (again, according to Wikipedia) was a heck of a lot faster than an average of 2,190 mph.

But, who knows? I could be completely wrong, since I'm half-blasted on liquid pain killers (JD) and needing sleep in a big way. I welcome your corrections to my facts, for when I'm alert enough to process them.

Still, it remains that you are right - it won't do escape velocity, won't go high enough, and can't operate outside the atmosphere.

[randwolf.livejournal.com]

The US news media has been letting go reporters at a great rate. Science reporting has been hit especially hard, see here (http://www.cjr.org/the_observatory/science_reporting_by_press_rel.php) (Columbia Journalism Review.) So, we get bad science reporting.

[unixronin.livejournal.com]

Good point. What's that line about crap always rolling downhill....?

[ithildae.livejournal.com]

First Rule of Plumbing. It rolls downhill.

Second Rule, Payday's Friday.

[smandal.livejournal.com]

A well-written essay (http://www.nytimes.com/2010/02/09/science/space/09essay.html) and attending impassioned comments at the New York Times.

I agree with the central theme of the piece: Apollo was a crash program meant to one-up the Soviets, but it was also immensely inspirational -- we can learn from both aspects. We don't have a Great Enemy to justify spending ~1% of GDP on a race, but we have to do better than missions that only satisfy PhDs.

So, what should budgetary priorities be? Unmanned scientific missions for sure, but I would add:

1. A tiebreaker in favor of inspirational and culturally significant scientific missions, like the Mars landing and Hubble. One idea would be robotic missions to search for life on outer moons.

2. A research program to address the technical issues of manned space flight, rather than rehashing 60's technology.

There should be a way to move into the future without replaying old glories or simply paying lip-service ...