Cheapest way ever to orbit

[rogers_buck]

I think I can promise that this is going to be the weirdest way ever to space. But I think it is sound, so here goes.<br /><br />The basic plan is to develop a tether of woven kevlar or maybe nanotubes. This is not your usual space tether plan though so read on. This tether will be clad in a thin ablative material with an outer coateing of PETN or other high-explosive and an outer jacketing material. You will need about 50Km of the stuff.<br /><br />You hook the end of your tether to a heavy lift high altitude balloon and let it go. After a few kilometers are played out you release a second baloon attached to the tether, You repeat this process until the first balloon is at its ceiling ~50Km and has migrated due east in the wind<br /><br />The end of the tether is attached to a payload of several tons. When the tether is at its desired attitdue and angle, the PETN coating on the end of the tether at the payload is detonated.<br /><br />The blast front propogates up the tether, blasting away the outter cladding and vaporizing the ablative coating on the inner load bearing cable and imparting forward momentum to the tether.<br /><br />The resilience or blast propagation speed of the explosive is tuned to the speed of sound in the tether. As the explosion propogates the energy is absorbed in the elasticity of the tether and thrust is ultimately imparted to the payload. By the time the explosion front propagates to top of the tether the payload (and it's end of the tether) is doing Mach 25.<br /><br />The tether can then be recovered and reprocessed for the next launch.<br /><br />In short, the tether acts as a long skinny ultra powerfull rocket engine that tows the payload to the desired acceleration using its inherint elasticity as an energy store.<br /><br />I'll leave it as an excersize for someone to work out the numbers. I'm going to go swimming.<br />

 

[scottb50]

So is this an Acme product? <div class="Discussion_UserSignature"> </div>

 

[rogers_buck]

Too safe for ACME, the explosion is heading away from you at several thousand feet/second.

 

[scottb50]

Beep- Beep! <div class="Discussion_UserSignature"> </div>

 

[rogers_buck]

>> Beep- Beep! <br /> <br />Wait til your in orbit Sputnik.<br />

 

[rogers_buck]

After a nice swim I decided I was all wet. (-;<br /><br />

 

[nacnud]

JP Aerospace is who your looking for.

 

[douglas_clark]

That JP Aerospace site is amazing! Sounds like we'll all be touring the solar system in eight years time. There must be snags, but surely somthing like that should be fast tracked?

 

[rogers_buck]

Way cool. Why haven't we heard about these guys?

 

[nacnud]

dunno, there has been a few articles about them on SDC before

 

[mrmorris]

<font color="yellow">"Why haven't we heard about these guys? "</font><br /><br />There's been an article or two on SDC and SpaceDaily. However -- they haven't *done* anything yet, so not much to hear about.

 

[radarredux]

> <i><font color="yellow">Way cool. Why haven't we heard about these guys?</font>/i><br /><br />Several of us (me included) have mentioned them several times in these discussion boards, and they have made at least one presentation at a space conference.<br /><br />The key is that they currently have contracts for this technology for <i>non-space</i> purposes. At this point the space part of their vision is only pretty pictures. My guess is that they are shopping the idea around to look for additional dollars, public support, or prevent support going to other parties (the Microsoft strategy); otherwise, I think they would keep this in house. [Note: If their Air Force contract is an SBIR contract, they are required to show how they can potentially derive additional revenue from the work they are doing for the Air Force]<br /><br />However, I think they are behaving like good business people: they are developing a core capability, and now they ask how can they use this for other streams of revenue.</i>

 

[rogers_buck]

I did some more mental simulations of this scheme and I think there needs to be a rocket up at the far end of the tether. The reason is that even though this system is a good approximation for a stretched rubber band the tether itself is not trully eleastic and will need to be kept straight during the accelearation of the payload. The rocket at the end of the tether will need to be able to accelerate the weight of the tether alone for a distance approximately 20% of the length of the tether. Not too bad.<br /><br />Assuming the energy transfer to the tether is 50% we can calculate the total energy available to accelertate the payload. Let's assume that their is 1g of high-explosive every centimeter of the tether. Since the tether is 50km in length that gives us 50*1000*100g or 5000kg of high-explosive. The total energy yield we take the heat of explosion at 3.2kcal/g and divide that by two (50%) we calculate that the explosive energy is equivalent to 73394.5kg of TNT (80.7 short tons). Given that TNT releases 2175 J/g that gives us a total energy of 159631950000 Joules.<br /><br />The impulse depends upon the resilence of the explosive, but lets assume 2km/s for our approximate PETN model. Given that the tether is 50km that makes the impulse 25seconds.<br /><br />The total thrust would then be 6000MJ/s for a distance of %10-20 the tether length. Which compares rather favorably to the shuttle SSME 1,856 kN.<br /><br />Of course for every G of acceleration the tether is far more likely to snap... But since the point of loading is moving so fast up the tether (maybe faster than sound) each point in the tether is stressed only briefly. At the time each point is stressed it is surrounded by a pressure wave compressing it. This might be tuned to point harden the active point on the tether as the maximum load gets applied. Weird.<br /><br />Edits:<br />I meant to say 5000kg not 5kg.<br />Screwed up the energy calculation by 3 order's of mag...

 

[mental_avenger]

<font color="yellow"> Because most of the cost of launching rockets into near space is escaping the first 20-30 miles of atmosphere and gravity, most of the cost of the launch is saved. </font><br /><br />Uh, I don’t think so, Tim. Starting at a high altitude, one above the limit for Max Q, allows the rocket to function more efficiently, that’s all. Very little overall energy is saved. For the STS, Max Q is about 3300fps at about 130,000 ft, about 1 minute after launch. Consider that a payload must be accelerated to ~17,400 mph (7.78 km/sec) A high altitude platform would be starting at ~1005.4 mph at best. Also, the very high altitude launch would only reduce the vertical distance by about 1/10th. (20 miles/200 miles)<br /> <div class="Discussion_UserSignature"> <p style="margin-top:0in;margin-left:0in;margin-right:0in" class="MsoNormal"><font face="Times New Roman" size="2" color="#ff0000"><strong>Our Solar System must be passing through a Non Sequitur area of space.</strong></font></p> </div>

 

[rogers_buck]

>> Very little overall energy is saved. <br />Quite a bit of energy taken raising a dead weight 100,000 ft. The engine efficiencies are a goodly % (I think over 2000MN for the SSME at altitude). But, as you say, you still have to get moving to get into orbit and stay in space.

 

[radarredux]

> <i><font color="yellow">you still have to get moving to get into orbit and stay in space.</font>/i><br /><br />One advantage of the JP Aerospace approach is that you do not need a high thrust engine to keep the vehicle off the ground. This gives you the freedom to use an Ion engine with low thrust but high ISP. It will take a long time to reach orbital velocity, but you will get there.<br /><br />A second advantage is that you can reverse the processes -- slowly deaccelerate and then float back down to earth. Everything is 100% reusable and there is no dangerous high-speed re-entry into the atmosphere.</i>

 

[rogers_buck]

No, I'm afraid gravity is still 1 G at 100K feet. Let something heavy go from your balloon without a big smokey rocket and it will fall like a rock.

 

[radarredux]

> <i><font color="yellow">No, I'm afraid gravity is still 1 G at 100K feet. Let something heavy go from your balloon without a big smokey rocket and it will fall like a rock.</font>/i><br /><br />Actually, gravity should be a little bit less, but the real key is that the payload and the balloon float together near the edge of the atmosphere. No propulsion is needed to keep it aloft. Just start applying some horizontal thrust (e.g., with an ion drive) to the balloon and payload, and slowly you build up speed until you reach orbital velocity.<br /><br />The balloon goes into orbit along with the payload.</i>

 

[rogers_buck]

I missed the part where the balloon + rocket gets accelerated. Intuitively, if the balloon is big enough to get lift from the air at that altitude, it is big enough to meet with significant wind resistance at that altitude. Maybe a set of giant gosamer wings would be more appropriate for lift and aerodynamic requirements. But even those would be a real problem for resistance at mach speed.

 

[jpowell]

JP Aerospace hasn't been pushing the media the last few years due to our DOD work.<br /><br />However, we have *done* a few things like flying over 80 development missions. These include Balloon platform rocket launches, 130,000 feet upper atmosphere infrastructure flights, three Vee airships, two Dark Sky Stations, a near space propeller validation, and 1600 student payloads to the edge of space.<br /><br />I think we may fly more than anyone in the business.<br /><br />JP

 

[douglas_clark]

Would be really interested in your response to rogers_buck's question about the aerodynamics of the ion drive to orbit proposal. It does seem to me to be the flaw in the arguement, but I'd really like to be wrong!<br /><br />Douglas

 

[bobvanx]

Ion drives are such a low-power thrust, that my intuition suggests it'd be overwhelmed by drag forces. In other words, the little bit of propulsion it offers is on the wrong side of the curve to lead to higher and higher speeds and altitudes.<br /><br />An engine that can overcome the vehicle's drag at low altitude, and keep that number over unity, clear to the top of the atmosphere, might get the job done. Maybe.<br /><br />Too bad nothing like that exists.

 

[mrmorris]

<font color="yellow">"I think we may fly more than anyone in the business. "</font><br /><br />My apologies. I didn't mean to imply that you were sitting on your hands doing nothing, just that you have not yet achieved the end-products mentioned in the post. When Ascender reaches orbit or you have a functional Stratostation in near-orbit -- <b>everyone</b> will be reading news stories about JPA.

 

[jpowell]

No apologies needed.<br />This is a very long project. We've been working on it for a 25 years now. We're about seven years out from the orbital Ascender. It works out to around 30 missions left. To us it seems like the home stretch, although I realize is a long time.<br /><br />We're gearing up for the next round of missions this winter. These will include a major upgraded Dark Sky Station and some other really cool stuff.<br /><br />JP Aerospace works in a small step by step approach. Frustratingly slow at times but we're getting there.<br /><br />JP<br /><br />ps. If anyone want to put something on one of our missions go to www.pongsat.com and ride along with us. (it's free).<br />

 

[mrmorris]

<font color="yellow">"If anyone want to put something on one of our missions go to www.pongsat.com and ride along with us."</font><br /><br />I saw this on your site and was interested. Of course I'm interested in a lot of things that I never get around to finding the time for...<br /><br />However, I was wondering if there was anywhere that had more details on some of the contents of previous pongsats. It'd be inspiring to read through such a list and think "Well that's interesting -- but what if you did <b>this</b> instead?"