J.JPM@LOTS-B (Jim McGrath) (01/07/86)
As much as I like to play with concepts such as 200 km long accelerators in orbit to boost sub-orbital payloads to low earth orbit, these proposals have usually left me with an empty feeling. The problem is that in order to construct such a large structure in space, you already have to have a good space transportation system. In other words, how do we get there from here? What do people think of the prospects of placing a SMALL accelerator into orbit, and using it to give a velocity boost to payloads coming from earth? This would still require some form of earth based accelerator system or the like, but over time you could, by building more orbital accelerators, reduce the velocity that needs to be imparted on earth. This would allow you to build more, cheaper earth based accelerators, and thus a positive feedback would begin. The question is, what is the maximum size (in length and acceleration) of an orbital accelerator that we could reasonaby construct using Shuttle or immediate post-Shuttle systems? And what is the biggest earth based accelerator/launch system that we could construct? Finally, can the first impart enough velocity to the second to make orbital velocity? Jim -------
space@ucbvax.UUCP (01/07/86)
There was a spaceport similar to your idea described in Analog a couple of years ago. Boosters are use to lift cargo up to orbital heights but without orbital velocity. Then the spaceport grabs it and accelerates it to matching velocity. When it's cargo is discharged, load it up with finished products (using garbage to top it off) and accelerate it out the end of the spaceport (maintaining the spaceport's orbit) and dropping the cargo gently in to the atmosphere.
mcgeer@JI (Rick McGeer) (01/07/86)
> >As much as I like to play with concepts such as 200 km long >accelerators in orbit to boost sub-orbital payloads to low earth >orbit, these proposals have usually left me with an empty feeling. >The problem is that in order to construct such a large structure in >space, you already have to have a good space transportation system. In >other words, how do we get there from here? > >What do people think of the prospects of placing a SMALL accelerator >into orbit, and using it to give a velocity boost to payloads coming >from earth? This would still require some form of earth based >accelerator system or the like, but over time you could, by building >more orbital accelerators, reduce the velocity that needs to be >imparted on earth. This would allow you to build more, cheaper earth >based accelerators, and thus a positive feedback would begin. > >The question is, what is the maximum size (in length and acceleration) >of an orbital accelerator that we could reasonaby construct using >Shuttle or immediate post-Shuttle systems? And what is the biggest >earth based accelerator/launch system that we could construct? >Finally, can the first impart enough velocity to the second to make >orbital velocity? > > >Jim >------- > > That's not really the problem. The problem is that mv = mv; in other words, any momentum change that you impart to the payload is also imparted to the accelerator and whatever it's anchored to. If the accelerator is earth-based, it's not a problem, since the momentum change is imparted to the earth, which is highly massive, and so the resulting velocity change is negligible. For a space-based accelerator, things are very different. With each outbound (inbound) launch, the accelerator's orbital velocity is reduced (increased) by an amount equal to dv (payload) * m (payload) / m (accelerator). One way of getting around this is to have the space-based accelerator fire off two payloads with every shot, with equal momenta changes in exactly opposite directions. In this way, the accelerator's orbit is kept constant. The two shots could be shuttle re-entry and lunar orbit transfer, for example. Rick.