From: vince@offshore.ai (Vincent Cate) Newsgroups: sci.space.tech Subject: Re: Lunar Sample Return via Tether References: <9186edb5.0312061749.206011fa@posting.google.com> <9186edb5.0312101 309.4509af66@posting.google.com> <3FD89AAE.5A716AE1@nospam.com> <9186edb5.03121 12210.6d51b0f8@posting.google.com> <3FD9C8E8.A32A0A08@nospam.com> <9186edb5.031 2132223.5573dfe3@posting.google.com> <3FDCFB2E.9EEB09F3@nospam.com> NNTP-Posting-Host: 209.88.68.33 Message-ID: <9186edb5.0312160716.397d2975@posting.google.com> Andrew Nowicki wrote: > PS. I would rather use tethers where they are needed the > most -- low Earth orbit. It is not like we have a limited amount of rope and need to choose one or the other. Also, the perception/reality that tethers are exotic and not yet used to do real work would totally change if a tether probe came back from the moon with more regolith than all rocket flights combined. > There is lots of massive junk there. Hook up a rotating > electrodynamic tether to the space station, and you have > a cheap space transportation system launching a few small > payloads a day to low Earth orbit and beyond. First, one might read that to mean you think the space station is junk. :-) My father published a paper on collecting junk for a tether ballast (copy on my site). He now thinks that if you have a reusable suborbital rocket it is better to just bootstrap your ballast starting with the empty rocket stage from the ELV that launched you to orbit (easiest piece of junk to get). Time is money and collecting more junk takes time. At first your suborbital RLV will not have full payloads, but even a mostly empty suborbital RLV should be cheaper per pound than any ELV. Also, you get to send up larger and larger payloads as the ballast grows, so you don't stay mostly empty for long. The pull of the tether on the ballast when lifting 1,000 lbs would be 10,000+ lbs (not only the payload but all of the tether mass and a maybe a couple Gs at the end). The space station can handle 870 lbs primary RCS thrust for 5.5 seconds or vernier RCS at 25 lbs for 130 seconds. But it is really designed as a zero-G structure and a continuous 10,000+ lbs thrust would probably snap off solar panels and maybe some modules. I suspect it would be hard to strengthen the station enough, and taking any risks with people onboard ISS is hard to imagine. Scrapping the space station and using it for ballast seems politically difficult. :-) -- Vince