Quote from: tvg98 on 06/25/2017 11:37 pmBased on some oversimplified assumptions for some calculations, it looks like that stage may have dropped 2-4 meters before hitting the deck. Does that sound right?Any landing you can walk away from...It will be interesting to see the deckside camera footage of the landing when it becomes available. Both today and Friday may have been "interesting" landings, and both should make for some good discussions once the video is out.
Based on some oversimplified assumptions for some calculations, it looks like that stage may have dropped 2-4 meters before hitting the deck. Does that sound right?
Quote from: mgeagon on 06/26/2017 07:19 amA ship at sea will rise and fall with the average swell of its cross-section. In heavy seas, swells can easily reach several meters and have periods of seconds to minutes. The rocket starts its landing burn and throttles to achieve 0 m/s at what it hopes will be the deck of the ASDS. If level off is achieved and the deck has heaved 2 - 4 meters below, the results must be engine shutdown and a hope for the best. Impact in this case seemed to provide a short bounce, but no particularly noticeable ill effects. I think the booster has an radar altimeter and should be able to measure rate of approach. It wouldn't even be that hard a piece of software to figure vertical barge movements into the decent if they were regular. Problem is of course, barge movement from swells isn't always a smooth oscillation and can be erratic, and different parts of the deck move at different rates depending on how the barge is pivoting. They could ballast the barge before landing to reduce movement, but you'd have to balance that against the risk of waves washing over the deck. And discharging ballast at sea has it's own complications and would add time to the operation. They're going to have a less than optimal landing eventually, and I can't help but think they really need a spare ASDS to keep the schedule up. There are too may reasons one might not be available for a launch, and that would mean underwater boosters until it was back online.
A ship at sea will rise and fall with the average swell of its cross-section. In heavy seas, swells can easily reach several meters and have periods of seconds to minutes. The rocket starts its landing burn and throttles to achieve 0 m/s at what it hopes will be the deck of the ASDS. If level off is achieved and the deck has heaved 2 - 4 meters below, the results must be engine shutdown and a hope for the best. Impact in this case seemed to provide a short bounce, but no particularly noticeable ill effects.
Nomadd, the ASDS is already ballasted. These converted Marmac 304 barges have flood-able tanks to allow it to be "in ballast". http://truesouthmarine.com/uncategorized/the-spacex-autonomous-spaceport-drone-ship/
Quote from: virnin on 06/27/2017 01:01 amI'm expecting grid fins to be reused more often than booster cores, just due to the elimination of refurbishment. Someone made a comment on SpaceflightNow that was funny but partly true. He said SpaceX will only need one set of titanium grid fins. Let's say 3, one for each launch site.
I'm expecting grid fins to be reused more often than booster cores, just due to the elimination of refurbishment.
Quote from: CyndyC on 06/27/2017 02:03 amQuote from: virnin on 06/27/2017 01:01 amI'm expecting grid fins to be reused more often than booster cores, just due to the elimination of refurbishment. Someone made a comment on SpaceflightNow that was funny but partly true. He said SpaceX will only need one set of titanium grid fins. Let's say 3, one for each launch site.Someone forgot about FH it seems.
Quote from: Lars-J on 06/27/2017 06:20 amQuote from: CyndyC on 06/27/2017 02:03 amQuote from: virnin on 06/27/2017 01:01 amI'm expecting grid fins to be reused more often than booster cores, just due to the elimination of refurbishment. Someone made a comment on SpaceflightNow that was funny but partly true. He said SpaceX will only need one set of titanium grid fins. Let's say 3, one for each launch site.Someone forgot about FH it seems. At least until they are flying every other day or so, and you don't have the time to grab the fins off the previous booster and mount them on the next.
With 2 pads shooting and the potential for several launches a week, ISTM they're going to need either more ASDS's or a much faster platform equipped ship/catamaran/?..? - or two.
Or RTLS. Block 5 may allow RTLS for Iridium NEXT launches. (speculation)
Quote from: Lars-J on 06/28/2017 04:49 pmOr RTLS. Block 5 may allow RTLS for Iridium NEXT launches. (speculation)Iridium launches don't seem that much heavier than Dragon launches, although they are going to higher orbit (~600km vs ~200km) and require a PLF where Dragon does not. I would guess that RTLS will be possible, given that RTLS of CRS missions is within Block 3 capabilities. But it might be a close shave.
The only figure I've ever seen (and I can't remember the exact number now, it was a tweet from Stephen Clark) I think was around 8600kg for a fully loaded Dragon? I don't know exactly what that included. If it included the trunk then Iridium is quite a bit heavier, especially before the fairing is dropped.
No Roomba either.
Quote from: docmordrid on 06/28/2017 07:47 amWith 2 pads shooting and the potential for several launches a week, ISTM they're going to need either more ASDS's or a much faster platform equipped ship/catamaran/?..? - or two.Or RTLS. Block 5 may allow RTLS for Iridium NEXT launches. (speculation)
Quote from: Lars-J on 06/28/2017 04:49 pmQuote from: docmordrid on 06/28/2017 07:47 amWith 2 pads shooting and the potential for several launches a week, ISTM they're going to need either more ASDS's or a much faster platform equipped ship/catamaran/?..? - or two.Or RTLS. Block 5 may allow RTLS for Iridium NEXT launches. (speculation)Theyre not going to sustain over a hundred launches per year before ITS or similar.