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Unguided orbital insertion (cheap upper stages)
On Feb 25 2002 John Carmack started a thread by this name. Google
won't let me reply to that thread so I am starting another by the same name. John Carmack: It seems to me like it is possible to put something into a 200km (or whatever) circular orbit with a simple unguided, spin-stabilized second stage, even when launched from an straight up/straight down booster with a 100km apogee. The idea would be that the X-Prize vehicle would have the passenger cabin replaced with a fairing over a 300kg, non-streamlined second stage mounted on a platform that could spin up and precisely aim it (nearly horizontally) before firing it while the booster still has significant upwards velocity. The complex stuff comes back down to be reused, and the second stage is basically a piece of ammunition. This is an interesting and fun problem, so I played with it a bit in my simulator. With a high G spin stabilized rocket I can get an orbit with a 90 km perigee. Depending on how high the apogee is, the mass, and the drag, this can last for a bit (just over a day in one sample I did). With a small thruster (Hall thruster /ion-drive/arcjet) on the payload it can easily raise the perigee and circularize the orbit. I don't think that with a spin stabilized rocket aimed at one point alone you can get into a 200+km circular orbit starting from a minimal X-prize vehicle (i.e. goes to just over 100 km). If you aim below horizontal by much you just hit too much air. If you aim above then as you start to go around the Earth the angle seems higher and higher relative to your velocity, which is not what you want. It makes it as if your orbit came from inside the atmosphere, and so after you get most of the way around that is where you will be. One trick (from Henry Cate) is that you could have your apogee kick motor in front of the payload aimed the opposite way so that when your spin stabilized vehicle got to the other side of the Earth it would be aimed the right way. I did this in one sample below. If spin stabilizing something can last for 40 minutes this could work. You want high G thrust, so you may need to go to solids. And if you go to solids you probably need 2 stages. But it seems like 2 spin stabilized solids and a small motor aimed backwards, or an electric thruster on your payload, and you could get to a stable orbit from an X-prize vehicle. This could be very cheap, and so seems like good idea. See samples 78 to 81 named "X-prize to orbit ..." in Java applet at: http://spacetethers.com/spacetethers.html -- Vince |
#2
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Unguided orbital insertion (cheap upper stages)
Henry Spencer:
[...] Finally, most prominently, Explorer 1 was put into orbit by an unguided three-stage solid cluster lobbed up to orbital altitude by a stretched Redstone. In all three cases, the launcher was guided, but the guidance system stayed behind after pointing and spinning up the upper stage(s). Nice that 3 stages of spin stabilized solid rocket were demonstrated 45 years ago. They were spun up to something like 750 rpm. Also they were high G stages, like X-prize to orbit would probably be. Payloads for this type of launch would have to be a bit more rugged than normal. Some time back I called up a company that makes solid rocket engines for model rockets and they were happy to make reasonably large engines, big enough for this, using lightweight cases (most model rocket engine cases are relatively heavy) for a price. Someone who can make a working X-prize vehicle should be able to purchase a couple solids (order of 150 Kg and 30 Kg) and make a spin stabilized 2nd and 3rd stage to get a small payload with a thruster into orbit. Fun fun fun. -- Vince |
#3
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Unguided orbital insertion (cheap upper stages)
In article ,
Vincent Cate wrote: One trick (from Henry Cate) is that you could have your apogee kick motor in front of the payload aimed the opposite way so that when your spin stabilized vehicle got to the other side of the Earth it would be aimed the right way. I did this in one sample below. If spin stabilizing something can last for 40 minutes this could work. Spin stabilization can last much more than 40 minutes, if the thing is balanced properly and is spinning around the right axis. Trying to spin a long skinny stack of hardware around its long axis, in particular, is a disaster. This may be a problem with two solids underneath the payload and an apogee motor on top. -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
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Unguided orbital insertion (cheap upper stages)
Vincent Cate wrote:
One trick (from Henry Cate) is that you could have your apogee kick motor in front of the payload aimed the opposite way so that when your spin stabilized vehicle got to the other side of the Earth it would be aimed the right way. BRBR This is exactly what the Navy guys from China Lake tried in the NOTSNIK launches of 1958. Looking only at the one or possibly two rockets that ever got to orbital altitude out of six launches (four tore apart or blew up) the problem was that there was no way for the satellite to know if it had the right orientation. Once the third and fourth stages were fired, the assumption was that the spin stabilization would keep it oriented correctly so that, when the kick motor fired halfway around the world, the thing would go into a circular orbit. But you had four staging events, each with a chance to impart a bit of unwanted motion. It may well be that on the most intriguing launch, when the New Zealand trakcing station detected the first-pass signal but never one from a second orbit, the satellite may worked, but have been pointing in the wrong direction. It may have burned directly into the atmosphere or launched itself into a higher parabola that still ended up in the atmosphere before a full orbit was complete. Or it may have expended the fuel on an unintended plane change, in which case it still ended up re-entering. I've always thought the audacious engineers and physicists behind this unique effort should have given up some altitude capability (they were aiming for a 1400 nm circular orbit) in exchange for a slightly heavier payload with a couple of photocells that might have made sure the kick motor fired in a useful direction. Matt Bille ) OPINIONS IN ALL POSTS ARE SOLELY THOSE OF THE AUTHOR |
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Unguided orbital insertion (cheap upper stages)
In article ,
Vincent Cate wrote: Finally, most prominently, Explorer 1 was put into orbit by an unguided three-stage solid cluster... They were spun up to something like 750 rpm. Also they were high G stages, like X-prize to orbit would probably be. Payloads for this type of launch would have to be a bit more rugged than normal. Likewise the rocket motors. At 700RPM, the centrifugal force on the Juno I second-stage motors was 180G! -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
#7
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Unguided orbital insertion (cheap upper stages)
On 10 Nov 2003 18:39:42 -0800
(Vincent Cate) wrote: snip This could be very cheap, and so seems like good idea. The only thing is that these days a guidance system doesn't have to be that expensive. Computers and GPS chipsets are pretty cheap now. Mechanical fabrication is still pretty expensive, though. But you are stuck with that. ---- Michael Smith Mail address and GPG key available from www.netapps.com.au -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.1 (GNU/Linux) iD8DBQE/s2GsVBAeZyhLJFgRAnJLAJ9gL7MOqNdmb6a05zOndllX+UAh9A CfdhEh BLPHjIPj//TdUk/AuLRmhUY= =7IFf -----END PGP SIGNATURE----- |
#8
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Unguided orbital insertion (cheap upper stages)
A slender, spinning projectile will work if it opens like an umbrella:
http://www.islandone.org/LEOBiblio/S...lla_projectile |
#9
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Unguided orbital insertion (cheap upper stages)
Talking about spin stabilizing solids:
Vincent Cate wrote: You want high G thrust, so you may need to go to solids. And if you go to solids you probably need 2 stages. My remembrance is that the delta velocity estimate for the spinning PAM-S burn for the IUS/PAM-S upper stage mission for the Ulysses spacecraft changed by over a thousand feet/sec once as close as one year to launch as the experts argued about the best assumptions to make about the effect of the spinning on the solid motor inerts. The PAM-S/ULS stack was going to be rotating faster than their existing information covered (70 RPM). This episode did not provide me a lot of confidence in the estimate . This change was only around for a short while, until the experts then argued themselves back out of it. As it happened, however, the final estimates were extremely accurate. Is there still uncertainty about this kind of effect with spinning solids, or perhaps this is only an issue with large motors? - Matt |
#10
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Unguided orbital insertion (cheap upper stages)
Henry Spencer wrote:
In article , Vincent Cate wrote: One trick (from Henry Cate) is that you could have your apogee kick motor in front of the payload aimed the opposite way so that when your spin stabilized vehicle got to the other side of the Earth it would be aimed the right way. I did this in one sample below. If spin stabilizing something can last for 40 minutes this could work. Spin stabilization can last much more than 40 minutes, if the thing is balanced properly and is spinning around the right axis. Trying to spin a long skinny stack of hardware around its long axis, in particular, is a disaster. This may be a problem with two solids underneath the payload and an apogee motor on top. Liquids are of course a real problem, as liquid filled objects tend to do odd things when spun. Diddn't the black arrow series of launches from the UK do essentially this? |
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