Here's a Google Earth comparison from 18 miles with the video when KSC comes into view. The engines are already firing before KSC comes into the frame, so the burn begins around 20 miles.
OK, a couple of things that I just can't believe. Real spacecraft designers please opine if you will!1. No switchguards around those center console buttons?
Quote from: Crispy on 05/30/2014 02:19 pmQuote from: sghill on 05/30/2014 01:52 pmHere's a Google Earth comparison from 18 miles with the video when KSC comes into view. The engines are already firing before KSC comes into the frame, so the burn begins around 20 miles.Without knowing the field of view for either camera, that comparison is effectively meaningless, unfortunately.How do you figure? The land mass would look stretched or shrunken if the field of view differed greatly between the two and it doesn't so the field of view has to be roughly similar. And since the land looks pretty close to the same in both images, the altitude must also be the same. In other words, KSC isn't going to look like that from 2 miles up (versus 20 miles) even with a fisheye lens.
Quote from: sghill on 05/30/2014 01:52 pmHere's a Google Earth comparison from 18 miles with the video when KSC comes into view. The engines are already firing before KSC comes into the frame, so the burn begins around 20 miles.Without knowing the field of view for either camera, that comparison is effectively meaningless, unfortunately.
Or it could be "artistic license" in the video, like dglow and mme said.
Why would the trunk be a part of it? It is expendable. I would think a trunk-less Dragon 2 would be a much neater suborbital hopper, even though its range would be just a few miles at best.
They might also want to stretch out the landing burn so they can fly out any aiming errors they have. Before the engines come on they only way to change the course is to orient the capsule. Which is something that might not give much control compared to having the super dracos on low thrust for a mile or so before they are needed to slow the capsule down.
Quote from: Lars_J on 05/30/2014 05:49 pmWhy would the trunk be a part of it? It is expendable. I would think a trunk-less Dragon 2 would be a much neater suborbital hopper, even though its range would be just a few miles at best. Think= "non-expendable" Trunk with extra propellant etc to provide more performance. Yes I know all the arguments against that for an Orbital vehicle
Is this an obstacle?: If the fuel is below the nozzles, how does it get from a tank in the trunk against both gravity and the acceleration from the super dracos?
So modemeagle posted this discussion with his simulation of a 10% to 20% thrust profileQuote from: modemeagle on 05/26/2014 12:53 amI am going to do my chart again as I did more work on the equations, which is going to effect the results. Here is a possible nominal profile with ignition at ~ 1,000 meters at 10% thrust with an increase to 20% for the final stop. This should allow plenty of time to check operation of the Super Draco engines and shutdown any that are not up to par. I think this also shows that very low thrust is needed for the final brake and touchdown. Starting the 10% thrust later and 20% sooner will use less propellant due to gravity loses.I suspect the excess delta-v remaining will be used up while dropping the horizontal velocity.The duration is ~17.6 sec. As modemeagle found the velocity never hits zero at 10% the remainder of the 26 seconds shown in tonight's video must be more 10% thrusting, pre-testing the engines with time to deploy the chutes, targeting for landing on the pad "like a copter" and generally reducing the BPL factor.Or it could be "artistic license" in the video, like dglow and mme said.
I am going to do my chart again as I did more work on the equations, which is going to effect the results. Here is a possible nominal profile with ignition at ~ 1,000 meters at 10% thrust with an increase to 20% for the final stop. This should allow plenty of time to check operation of the Super Draco engines and shutdown any that are not up to par. I think this also shows that very low thrust is needed for the final brake and touchdown. Starting the 10% thrust later and 20% sooner will use less propellant due to gravity loses.I suspect the excess delta-v remaining will be used up while dropping the horizontal velocity.
More than 5 km sounds very careful considering that the drop test was at less than half that (8000 feet)
Quote from: eriblo on 05/31/2014 12:48 amMore than 5 km sounds very careful considering that the drop test was at less than half that (8000 feet) But the drop test didn't start at terminal velocity either.