Orbital Assistance

[alonzofyfe]

Question:<br /><br />What would be the possibilities for a system for getting people into space that operates as follows:<br /><br />(1) Using a SpaceShip2 type configuration, an airplane takes off, approaches the equator, turns east, then launches a rocket.<br /><br />(2) The rocket engines take the rocket to the edge of space, but does not actually reach orbital velocity.<br /><br />Instead, the launching spacecraft meets up with a 'tug' in space that grabs on and provides the extra thrust needed to reach a space station in low equatorial orbit.<br /><br />Advantage: the fuel and materials needed to provide the additional acceleration need not be lifted into space along with the payload. This saves both the weight of that last bit of fuel and the weight of getting that fuel to where it will be used. However, it requires the working assumption that fuel provided by a tug would be less expensive than fuel launched with the rocket. Is this a realistic assumption?<br /><br />Disadvantage: Risk/complexity. A failed rondezvous means an aborted mission. Naturally, a passenger ship would then have to survive re-entry.<br /><br />If this method is feasable, what would such a craft be like? Do the fuel requirements involved for taking passengers into space actually prohibit something like this?

 

[docm]

The tug must be orbital, therefore there will be a significant velocity difference between these craft by definition. This means one of two things must happen for them to dock;<br /><br />1. the rocket must speed up to meet the tug.<br /><br />2. the tug must slow down, effectively deorbiting, then re-boost itself and the rocket to orbit.<br /><br />Neither makes sense. <br /><br />If the rocket speeds up to meet the tug then the latter was obviously unnecessary to begin with. <br /><br />If the tug has to deorbit then re-boost I can't see how that is efficient at all given how much fuel it would take to perform both maneuvers <i><b>and</b></i> refuel the tug with yet another launch for the next few rounds. <br /><br />IMO 'tis better to just give the rocket another stage to begin with, presuming the carrier craft can still lift the stack. <div class="Discussion_UserSignature"> </div>

 

[jimfromnsf]

This is like another idea that was unworkable<br /><br />Reaching Orbit With an Assist<br /><br />http://uplink.space.com/showthreaded.php?Cat=&Board=businesstech&Number=712967&page=&view=&sb=&o=&vc=1

 

[docm]

But a capsule like t/Space's CXV could and have the "care-free" return. It too would be drop launched using the AirLaunch booster. <div class="Discussion_UserSignature"> </div>

 

[j05h]

The only place I can see this fitting is for the circularization burn - and then it would be a very dangerous maneuver with crew. Better off to have an extra stage or service module. <br /><br />You may be thinking of the proposed "Parom" tug. This would meet a cargo pod in a low orbit and move to a higher station orbit. This would enable larger per-launch payloads for Soyuz-class boosters, IIRC.<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[kelvinzero]

<blockquote><font class="small">In reply to:</font><hr /><p><br />1. the rocket must speed up to meet the tug. <br />2. the tug must slow down, effectively deorbiting, then re-boost itself and the rocket to orbit. <br /><p><hr /></p></p></blockquote><br /><br />hehe.. you missed one important case:<br /><br />3. the tug is thousands of kilometers long<br /><br />Which brings us to the orbitial loop idea. Personally I put this concept ahead of the space elevator.<br />Something for the future, ie when we have a huge moon industry spitting millions of tons of iron into orbit.<br /><br />There was also my plan for a ring of orbital atmosphere gatherers all spitting out a puff of gas or snow to hit the craft as it passes as an orbital velocity gale.. for some reason that idea was not well recieved <img src="/images/icons/laugh.gif" />

 

[vogon13]

Have Space Ship 2 dock with the bottom end of a space tether.<br /><br />Lowest 100 km is the toughest to build in any regard, so we just don't, and let SS2 fill the gap.<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[alonzofyfe]

Actually, I was thinking about the "slowing down, grab the ship, then speed up" option.<br /><br />The difference, as far as I could see, is:<br /><br />The cost of slowing the tug, docking, and accelerating to orbital speed.<br /><br />versus<br /><br />The cost of launching enough fuel to get to orbital speed to what would have been the rondezvous location.<br /><br />Slowing down the tug need not require fuel (or as much fuel) - but could use a catapault system on an orbiting station. This would also boost the station but, for a station in low earth orbit, an occasional boost is not necessarily a bad thing.<br /><br />The construction costs to reinforce the station would likely be prohibitive, however. Much will depend on relative differences in mass.<br /><br />For the rest of it, the system would use space-manufactured fuel.<br /><br />Now, in speaking about a spaceshiptwo style spaceship I was thinking actually about airborn launch. For re-entry, I see no particular reason not to use a capsul.<br /><br />However, for an airborn launch system, can such a system even lift something that could put people into orbit? Would the orbital craft be too big?<br /><br />What if launch mass is reduced by using the space tugs mentioned? Then, what would airborn launch be capable of?

 

[MeteorWayne]

Wow, you dismissed this particular hurdle pretty quickly <img src="/images/icons/smile.gif" /><br /><br />"For the rest of it, the system would use space-manufactured fuel. " <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[nrrusher]

With regards to a space hook/elevator, why not a combination?<br /><br />Granted, material strength is supposedly beneath the demands of a full length space elevator. What would stop us from building a partial one? For instance, with the center at GEO, having legs in toward earth and outward at a length of say 10,000 miles each way. <br /><br />Whatever our current abilities would allow, we could build. Launches to GEO would only need the fuel to just latch onto the bottom end, as the rotational velocity relative to the equator would match. Moon launches would be considerably cheaper. Mars/Venus launches could tarry out to the end to take advantage of a little rotational boost..... etc.

 

[jimfromnsf]

Because it is not anchored, it is not stable and the CG changes as the object climbs

 

[jimfromnsf]

"Actually, I was thinking about the "slowing down, grab the ship, then speed up" option."<br /><br /><br />Read this thread, like I said I in an earlier post. <br />http://uplink.space.com/showthreaded.php?Cat=&Board=businesstech&Number=712967&page=&view=&sb=&o=&vc=1<br /><br />It is not possible to slowing down, grab the ship, then speed up

 

[nexium]

Do the letters CG mean center of gravity? We can build a bolo = rotating tether perhaps 100 kilometers long. It is in LEO = Low Earth Orbit. It rotates end over end perhaps 6 times per hour C = 3.14 times the diameter = 314 kilometers v = 6 times 314 = 1900 kilometers per hour. We attach at the low speed bottom end at an altitude of about 150 kilometers, and release near the high end = 464 kilometers altitude at significantly higher speed. Not a big boost, but making the bolo longer or faster rotating increases the delta v proportionally, but requires stonger tether material. If the bolo has tip motors a short burn can reduce the jerk, fine tune the aim of the release, and restore the energy removed from the bolo by the payload. The bolo can also decelerate space craft returning to Earth. Slower at the low end means the tip can catch the pay load at an altitude of perhaps 50 kilometers without burning up in the atmosphere. Neil

 

[kelvinzero]

yes AlonzoFyfe, definitely read that thread.<br /><br />The real effort in getting something to orbit is the effort that goes into getting up to orbital velocity. Once you deaccelerate this tug you have thrown this advantage away, while still having added the effort of slowing the tug and docking the two.<br /><br />We have mentioned other ideas that get around this though. They might be impractical for other reasons but you can still have fun with the maths.<br />

 

[jimfromnsf]

The problem is there is only a instant (seconds) that the launch vehicle can meet the tether. It is not enough time to make corrections to set up the docking<br />

 

[kelvinzero]

Im almost afraid to get into this, but what if instead of a tether you have many tethers forming a cobweb-shaped disk that rotates like a wheel with the lower edge stationary wrt to the road? This would change the problem from intersecting a point at a precise moment to being anywhere along a line.<br /><br />I dont think this would necessarily be much more massive. Each individual thread would be much weaker than what is required to support the payload but crossconnect to distribute the load. <br /><br />Also the entire contraption would be quite springy. There might be some way to coax the lower edge to flattern out the way a car tire does, so the point of contact with the road is increased.

 

[jimfromnsf]

flattening is not possible, tethers can't take slack. Unless the perimeter is solid, it still is intersecting a point at a precise moment for a spoke

 

[scottb50]

I've been thinking more along the lines of a re-usable re-entry shield that gets through the main heating area, releases a landing vehicle and returns to orbit for re-use.<br /><br />Getting to orbit using multiple stages makes the most sense, the real problem is returning. If you descend to say 70-80 miles and turn the lander loose it would take the equivelent of an upper stage to get back to orbit. If a upper stage is the same thing as a Tug you build a heat shield, attach the Tug and Lander to it and use it over and over again.<br /><br />The lander could even be a modified version of a business jet, requiring minimal TPS aling the lines of Spaceship 1. <div class="Discussion_UserSignature"> </div>

 

[kelvinzero]

Yes I was thinking solid so that connecting might be more like a disk brake. Given the scale, I guess it would be like a vast knife edge coming down, slowing to a stop and reversing direction.<br /><br />Im pretty sure you yourself could think up a configuration of the mesh that could flex. It doesnt need to be spokes to the center. Other configurations would provide cross connection. But it isnt vital to the idea, especially if the 'disk brake' doesnt need to grab at exactly the right height.

 

[jimfromnsf]

"I've been thinking more along the lines of a re-usable re-entry shield that gets through the main heating area, releases a landing vehicle and returns to orbit for re-use."<br /><br />where is the advantage? Just more complexity without an benefits

 

[alonzofyfe]

Okay, let's say that orbital assistance at the high end is impractical. The rocket is better carrying the fuel it needs with it rather than picking up a packet of fuel once it gets into space.<br /><br />So, what about the aerial launch. Is that feasible for a passenger rocket going to orbit?<br /><br />How feasible?<br /><br />(How many passengers? 0?, 4?, 127.6?)<br /><br />Let us assume, for the sake of discussion, a capsul- like re-entry. The rocket body itself will - in part - stage away during launch and float back to Earth, or stay in space and be cannibalized.<br /><br />

 

[jimfromnsf]

"So, what about the aerial launch. "<br /><br />???? iit happens all the time with Pegasus. A passenger spacecraft will only be limited by the size of the drop aircraft.

 

[j05h]

<i>> The problem is there is only a instant (seconds) that the launch vehicle can meet the tether. It is not enough time to make corrections to set up the docking </i><br /><br />There's another issue besides the precise meet-up timing between payload and bolo. It's also the sudden, violent, probably off-axis nature of the payload's new acceleration. The system as described is an instantaneous meeting of a bolo grapple travelling +2000mph relative to the ballistic arc of the payload. Any way the difference in velocity is lessened brings the payload closer to orbit or drops the bolo that much closer to reentry, you might as well just use a normal third stage. Parom-type tugs meeting an already orbiting payload make much more sense. Tugs have their place, but it's once in orbit and beyond, not diving into the upper atmosphere for risky dockings. <br /><br />With a bolo design, attempting to make a mechanical shock absorber is going to always weigh more than simple rockets. <br /><br />Tethers are still a largely unproven technology. There have been many examples flown, and more upcoming, but all have been experimental. It is challenging enough to just build a tether that can survive in LEO. Most have snapped during flight. Dr. Hoyt's efforts are probably the furthest along for both weight-bearing and electrodynamics. <br /><br />Another form of orbital assitance could be a chain of equatorial gigawatt lasers serving as the second and third stages of an airlaunch system. Imagine a cross between Marshall Savage's Bifrost Bridge, Mirabo's Lightcraft and any kind of air-dropped rocket. No need for magnetic-levitation tracks if you deploy at 60,000ft and the lasers are currently closer to reality than any Bolo. <br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[alonzofyfe]

<i>iit happens all the time with Pegasus. A passenger spacecraft will only be limited by the size of the drop aircraft. </i><br /><br />That's my question: how big would a drop ship have to be to drop something that can put, say, 8 people in orbit, with a capsul, that can drop them back down to earth? Would the mass make any type of air launch prohibitively large?

 

[jimfromnsf]

do the calculations and tell us