Airbags, parachutes, Rogallo wings and all that

NASA of the sixties reminds me of the Armadillo Aerospace of today.
Drop tests, I think an F-111 model and various parachute, parawing and Rogallo wing things.

Airbags, landing rockets, landing gears (Dyna-Soar like rig)

Thank you NASA CRgis for another video blog day, one of many more to come!

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Random video blogging

Modern manufacturing technologies enable strange shapes and could produce unconventional pumps. What is good for small scale rockets if turbines and centrifugal pumps have too much tip losses?

Rotary engines have vastly better power to weight ratios and vibrate less than piston engines. They’re also expensive and hard to build (cue modern manufacturing again). Here is one demonstrated in a paramotor, Parajet Cyclone using a Rotron engine. Love the music.

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Spaceshiptwo – First Glide

Watch in high res at youtube. White Knight Two doesn’t look so large span after all. Spaceship Two is pretty wide with its outset elevons and the WK2 outer wings need to have the engines so there’s not much wing outside with the single purpose of lifting (or stopping the tip vortex). It seems both planes are really light too. Carbon fiber throughout. SS2:s wheels are really tiny. They have gone for minimum dry mass. The landing speed doesn’t seem huge even with its low aspect ratio. Maybe the size misleads. The landing is very smooth.

Of course the couple climbs out very fast even with gear out since SS2:s tank is empty and it doesn’t have the solid fuel onboard either.

I’m reminded of the lifting body research of the sixties. Who says we aren’t experiencing the golden age of aerospace right now? There’s happening interesting stuff left and right now, most of it in the more modest programs.

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Parawings and Rogallo wings, again

Inspired by Michel Van (not Scott Lowther as mentioned earlier) at Secret Projects, who ran into the Gemini inflatable Rogallo wing test videos that are now available (not embeddable so linked only). There are parafoil systems for airdropping stuff, though they don’t seem to be doing flares or line pulls to soften the impact:

And if somebody says parafoils are not maneuverable, I give you a Russian self built RC parafoil:

Speaking of rocketry, a member from the local hybrid group said they have found out the probable cause of roll control problems: the forward fins that were put on the rocket for roll control cause huge vortices when deflected, so that they effect the main fins far aft and the effect might be the opposite from intended.

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The Turn-Boost-Glide-Back approach for first stages

In a patent by the famous Barnaby Wainfan. EDIT: corrected the link. This patent was filed in 2006 and granted in 2008.

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Rockwell X-33 Pictures!

From NASA Langley – they did wind tunnel tests on a model. Lots more pictures of various aerospace projects there too, some of them are quite weird. Thanks to Secret Projects forum for the info!

Naturally since Rockwell built the orbiter, this one looks like the orbiter too. With an SSME and RL-10:s (so Rand.org says) and cylindrical tanks, it would have been far lower risk than the Lockheed version that won.

In a sense, the “almost pure rocket” cone, the “flies a little better than a rock” lifting body and the “almost flies like a dangerous plane” winged vehicle are the three main paradigms to reusable vehicles.

Though, with SHARP (or like McD did with active cooling), your lifting body can be sharp edged and have vastly superior L/D compared to blunt ones.

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Automotive X-Prize Winners

Huh, it always takes a long time to find anything on web pages that are so cluttered up. Here. No idea what the MPGe or miles per gallon equivalent is.

EDIT:

Here’s ERA’s video (they didn’t win, although they were very close. I think they were penalized for driving too fast):

Holy crap. Their vehicle has 1000 Nm torque and does 0 to 100 km/h in 6 seconds.

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On Pressure Fed Rockets and Scaling

Well, scaling seems to be my pet issue. I recently wrote something not entirely well reasoned in a comment at Paul Breed’s. (For some reason Chrome complains about blogrolling.com malware there so continue if you’re sure you’re safe.)
So let’s make it better. (A word of caution though, I’m quite sleep deprived now.)
For those who like to jump into conclusions, it’s going to be like this all over again.

Assume a pressure fed rocket first stage has a certain propellant chemistry, tank and thus chamber pressure and must operate in the atmosphere, hence has a certain exit pressure (0.1 MPa or 1 bar or 15 psi is the optimal). Then it has certain thrust per nozzle area.

Now, the rocket needs thrust to lift off. If we assume a constantly scalable shape, its mass will be base area times length times density.

Since the maximum fittable nozzle exit plane also depends on the base area, we find that for a certain area, the rocket can only have so much mass – or that the rocket has a maximum density times length parameter. If we assume the propellants have been picked early on, density is set and the rocket only has a height constraint.  Each pressure and propellant chemistry basically has a “characteristic length” that can’t be exceeded. Otherwise it can’t lift off.

The higher the exhaust velocity, the smaller the nozzle, so raising chamber pressure reduces the needed nozzle size per thrust and the rocket can be lengthened.

For small rockets, I’d hunch that they have little length and thus they don’t really have to worry about this. They can be as thin (and thus long) as practical, to try to avoid drag losses.

For upper stages, the thrust to weight needed is less and the weight even less so it’s even less of a problem – except that the expansion ratios can be huge since there’s no back pressure anymore. Still, with small rockets, pretty huge expansions might be possible without having much problems because the second stage is very small (=also short) anyway and thus there’s little mass per nozzle exit plane area.

On really tall rockets like Saturn V, the thrust per base area has to be huge, hence it had to have those base extensions for the corner engines (note how the N-1 had a conical shape with a wider base, the engines had a bit higher pressure but the upper stages were kerosene – these cancel out a bit but the base of the rocket had some empty space) . Similarly with STS, putting so much thurst on the tiny orbiter’s tail required high chamber pressures and some tail shaping

I don’t have any numbers handy, but if we assume a 10 m tall 1000 kg/m^3 density (water) rocket, then it has 10,000 kg per m^2 or the thrust required for a 20 m/s² acceleration is 200,000 N/m^2. This is easily achievable. With an exhaust velocity of 2000 m/s, the mass flow needs to be 100 kg/(s*m²) to produce that thrust. Again with the exhaust velocity that mass flow means a density of 0.05 kg/m^3. Air’s density is 1.2 kg/m^3 at 300 K, so that’s 20 times less dense which means hotter, the density is like hot air at 6000 K. Though the molecules might be mostly lighter OH instead of N2 and O2, making that rocket exhaust at 3000 K for the density. Rocket exhaust isn’t that hot – it’s cooler and denser and thus more thrust per unit area.

For a second stage we can look at the pressure fed AJ-10 from Delta 2: 1.7 meters diameter (certainly constrained), 40 kN of thrust. For a T/W of 1, density of 1000 kg/m^3, we get 4 tonnes and 1.7 meters of depth. Quite a stubby stage with a roughly spherical tank! Isp is 321 s. The real Delta II second stage weighs 7 tons and the payload is some too, but reusable rockets won’t have such high performance first stages (nevermind solids!), so they might need more T/W.

Oh, BTW, I assume three stages to orbit for pressure feds though I haven’t looked it that closely.  Mass ratios and ISP:s I’ve only hunched.

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Humans Fast, Machines Slow

Rand Simberg talks about impedance matching. So I’d like to make a post of my comment there (I’ve always wondered why this obvious alternative gets mentioned so little…)

What to do when you arrive at Mars or Earth with your solar electric propelled vessel?

So, the problem with most low fuel demand velocity change schemes is that they only give slow accelerations. Low fuel high velocity change means solar or nuclear electric propulsion and aerocapture mainly.

High delta vee aerobraking is hard to do in one pass – it gets dangerous because of atmospheric variability and potentially other reasons.

Simple: detach a small capsule with the humans that goes directly to the surface (with only days of life support) and leave the untended craft to do multi-pass aerobraking. Hitting van Allen belts a few more times or taking a long time doesn’t matter that much with no humans onboard.

You could also potentially ultimately leave the long distance craft at some Lagrange point instead of LEO. (Cue some clever and complex maneuvers to save fuel – maneuvers that take long.)

Something similar could also be done when a long distance stack is assembled in LEO: send the humans there only after it’s through the belts. They can go with a smallish capsule again. Potentially at some Lagrange point, or in space without any fixed reference, just along the way. It could be dangerous though if the capsule doesn’t have much life support.

Many of these things have potential delta vee penalties as well as timing inflexibilities, but they could have enough other benefits that they should be considered.

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There’s No Such Thing As A Reasonable Price Launch

Apollo 11 JSC KSC Flight Control, pre-launch

All these people had to get paid. Even when there wasn’t a launch. Well, to be exact: until the money was spent and there weren’t gonna be any more launches, which was a few years from this photo.

From the new NASA Flickr database.

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