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Several folks have commented on kick stages and tugs for BFS cargo. Some stuff from reddit and NSF : https://www.reddit.com/r/SpaceXLounge/comments/7553za/wildass_speculation_thread_20_3b_whoops_i_dun/ https://www.reddit.com/r/spacex/comments/9hys4y/bfr_gto_trajectory_ideas_with_falcon_9like_kick/ https://forum.nasaspaceflight.com/index.php?topic=46412.0 I am interested in reusable methalox kickstage designs that can deliver a 7 tonne sat out to GTO (2500m/s), then 16 hrs later at perigee burn back into LEO (another 2500m/s sans payload) for a later pickup and return to surface. cluster while waiting for pickup in LEO can be carried in a carousel on bfs cargo Why return to surface? Refuel in orbit might be doable...but payload transfer from BFS to kick would be tricky. Would need an extra berthing system. Keep it simple. Just do integration and fueling on the ground and wear the price of lifting 5t extra dry-mass on your 120t lifter. For example 12t of sub-cooled methalox (tanks are ~2m long by 3.0m diameter or another combination with gives ~14 cubic meters of tank space), 1 tonne dry mass (~7.7%), 10t raptor (100kN, sea-level for simplicity - 356s in vacuum, mass ~50kg) Solar / batteries / apu for 16hrs of operation and maybe a few weeks of dormant operation while waiting for pickup. Boil-off management up-to 90 minutes for GTO burn fuel(~11t) and ~16hrs for LEO return fuel(~1.1t), maybe 150hrs for clustering fuel. various attitude and ullage thrusters payload up to 7t Total package ~20t. 2018 BFS cargo (120t LEO) could lift a carousel of 5 or 6 of these. Dump them in LEO, let them GTO burn when they are in position, pickup a cluster of spent kicks from the last mission, and return home for dinner. Ideas/Comments?

So, I wanted to make an 'all in one' tug/explorer (vanilla parts) to export almost all of the Kerbol system. Criteria was that as much of the ship as possible should be reusable at each stop, and it can refuel itself along the way. My plan was to have three main components: a driller (for refueling), a science lander, and a tug to transport the other two components. The driller was pretty simple, with a 4500 ore capacity: Note the large docking port atop, that will mate to the 'back' of the tug. The harder part was building a lander. I started a lander that would handle MOST of the standard planets (Mun, Eeloo, etc) a single stage land/takeoff that would have about 3000+ dV. Added chutes and drogues for Duna and Laythe. For Duna and Laythe, I added a removable inflatable heat shield, connected with a docking port so I could add or remove it as the mission required via a docking port: Experimenting with the inflatable shield was VERY interesting. A few lessons: If you inflate it and it touches an atmosphere, you can't deflate and re-use it. Which means I'd need to bring one for Duna and one for Laythe. When you deflate it, it *VIOLENTLY* explodes. So I separated it as much as I could, and experimented to make sure after the peak of re-entry heat, I could turn the ship prograde, drop the shield, and then flip back retrograde before finishing the landing sequence (in some cases just turning sideways and firing the engines to get the heck away from this giant bomb I'm carrying). Otherwise, the air resistance forces the shield back into the craft, with another BIG BOOM. So, that being said, my tests with Laythe still didn't work because of the high dV needed to push through the atmosphere. So, I added another optional stage I could also add with a docking port: It's super ugly, and the lower engines gimbal way more than they should, making it a difficult craft to control. But I get an extra 1630 dV from the lower stage, coupled with 3670 on the upper stage (if I use the drop tanks, but a bit less otherwise), gives me about 5300+ dV total, enough to land and take off from Laythe and Tylo. Note that I have to cut the fuel cross-feed (otherwise it robs the upper tanks first) and the stage cutover is a manual redocking/staging sequence, but not too awful. So, now I have all the planets covered, except for Eve, of course. So, here is the assembled tug, powered by a dozen nuke engines: Note the two 'extra' sections being carried: - Fuel/Engine set for Tylo - Thermal balloon for Duna - Another set of both for Laythe And, of course, a science lab. Fully assembled and fueled, she has about 5000dV. Getting ready to run the full system test!

So as I've been building my latest space station, I've been streamlining it and removing the "self-flight" capability from pretty much everything and started moving more and more heavily into using tugs. Now for small, 0.625m and 1.5m things, the spider tug I got here on the forums has been a great reliable ever since 0.23.5. But with 2.5m and larger, I just don't really have good movers, so I'm trying my hand out at designing a reliable workhorse. Since it's supposed to be a tug, which basically means a space bulldozer, I slapped a great big engine with a good sized tank on it. 2.5m main docking port since that what I need it for with capability for drop tanks, but the placement of certain things like the SAS modules for stabilization and thrust burning has me a bit stumped. I dropped a bunch of radio's onto it because I really like RemoteTech, so I have a clipped/offset Communotron 16, a pair of DTS-M1's and a Communotron 88-88 for short/mid/long range comms so I can tug things all over Kerbol space. Advice/Suggestions welcome on my tug, so I can tweak it. Core Tug Tug with drop tanks Generic space station component, that my tug would be moving frequently.