Could SuperDracos be used for both retropropulsion and landing? If you want to use them for landing anyway it might make sense.
Would Kestrels would make good landing engines? They don't use turbopumps, right fuel, thrust seems in the right range for landing, and they're already a proven technology for SpaceX. Instead of using dead weight for ballast in the nose, that space could be a tank, fuel could be pumped between ballast and main tanks to shift center of gravity so your landing fuel is also your ballast.
no. The delta-v difference between a GTO that has pegiree of 70km (goes through the atmosphere so re-enters) and a GTO that has a pegiree of 300km is very very small, something like some tens of meters/sec. If a payload can raise it's orbit from 300km pegiree-GTO to GEO it can also raise it's orbit from 70km pegiree-GTO to GEO(unless it uses electric propulsion). Delta-v is not the problem here.
The problem is more about the reliability and orbit flexibility side than delta-v side. It might be beneficial to stay on the GTO for multiple orbits, not circulizing the orbit to GEO on the first orbit, to get to correct position on the GEO.
On a trajectory that has pegiree of under 100km this is not possible. And if there is some technical proplem delaying the circularization burn, re-entering after one orbit is also quite a bad thing.
Quote from: wes_wilson on 04/13/2017 12:06 pmWould Kestrels would make good landing engines? They don't use turbopumps, right fuel, thrust seems in the right range for landing, and they're already a proven technology for SpaceX. Instead of using dead weight for ballast in the nose, that space could be a tank, fuel could be pumped between ballast and main tanks to shift center of gravity so your landing fuel is also your ballast.The problem with a pressure fed engine is the additional mass for the propellant tanks, since they have to be at higher pressure than the combustion chamber.Another option might be electric pumped. The Rutherford engine by Rocket Lab has similar thrust to Kestrel, is 3D printed, and uses kerolox. If SpaceX wanted another engine of this type it likely wouldn't much harder to develop than SuperDraco, or they might license Rutherford from Rocket Lab. SpaceX typically doesn't use 3rd party engines but I think that's mostly because 3rd party engines cost too much and don't do enough to optimize manufacturing, neither of which is true here.
Quote from: hkultala on 04/12/2017 09:13 pmno. The delta-v difference between a GTO that has pegiree of 70km (goes through the atmosphere so re-enters) and a GTO that has a pegiree of 300km is very very small, something like some tens of meters/sec. If a payload can raise it's orbit from 300km pegiree-GTO to GEO it can also raise it's orbit from 70km pegiree-GTO to GEO(unless it uses electric propulsion). Delta-v is not the problem here.My point exactly. The payoff with this is no propellant needed for the de-orbit burn.
Quote from: ArbitraryConstant on 04/13/2017 05:38 pmQuote from: wes_wilson on 04/13/2017 12:06 pmWould Kestrels would make good landing engines? They don't use turbopumps, right fuel, thrust seems in the right range for landing, and they're already a proven technology for SpaceX. Instead of using dead weight for ballast in the nose, that space could be a tank, fuel could be pumped between ballast and main tanks to shift center of gravity so your landing fuel is also your ballast.The problem with a pressure fed engine is the additional mass for the propellant tanks, since they have to be at higher pressure than the combustion chamber.Another option might be electric pumped. The Rutherford engine by Rocket Lab has similar thrust to Kestrel, is 3D printed, and uses kerolox. If SpaceX wanted another engine of this type it likely wouldn't much harder to develop than SuperDraco, or they might license Rutherford from Rocket Lab. SpaceX typically doesn't use 3rd party engines but I think that's mostly because 3rd party engines cost too much and don't do enough to optimize manufacturing, neither of which is true here.That miniature Raptor/methane/BFS idea is looking better all the time...
Question how does S2 attach to dragon capsule now? With the heat shield sort of in the way? Maybe around the edges?
Quote from: rsdavis9 on 04/13/2017 08:07 pmQuestion how does S2 attach to dragon capsule now? With the heat shield sort of in the way? Maybe around the edges?The S2 attaches to the trunk, which attaches to the dragon with the attachment points on the bottom: http://i.imgur.com/s7yORbX.jpg
Quote from: CharlieWildman on 04/13/2017 04:32 amCG with out nose weight looks quite scary to this untrained eye. Adding 5 tons of nose weight gets it looking possible. Maybe it wont take 5 tons. Maybe just 3 tons... But still... Yikes!To me it looks better than expected. Instead of ballast at the top drag devices at the back will be much lighter and get it stable as well. Drag and steering plates folding out at the bottom are quite simple and lightweight. They need to be covered with PicaX heatshields.
CG with out nose weight looks quite scary to this untrained eye. Adding 5 tons of nose weight gets it looking possible. Maybe it wont take 5 tons. Maybe just 3 tons... But still... Yikes!
Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh. Is PicaX density known? Couldn't find it searching the web.
One improvement that PICA-X represents is greater ease of manufacturing. Like many things at SpaceX, PICA-X is made in-house and at a fraction of the cost of NASA’s PICA. Produced in large pieces and then cut into tiles about the size of a cafeteria tray they are placed, in a similar fashion to the MLS shield, on to a carbon-composite mold. The tiles are about 3 in (8 cm) thick, and weigh about 2 lbs (1 kg).
Quote from: CharlieWildman on 04/13/2017 11:49 pmPlanning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh. Is PicaX density known? Couldn't find it searching the web.I saw it mentioned a few days ago. But my poor memory has only slightly denser than balsa wood. I am pretty sure it is 0.38g/cm³ or close, really that light.
Quote from: guckyfan on 04/14/2017 06:38 amQuote from: CharlieWildman on 04/13/2017 11:49 pmPlanning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh. Is PicaX density known? Couldn't find it searching the web.I saw it mentioned a few days ago. But my poor memory has only slightly denser than balsa wood. I am pretty sure it is 0.38g/cm³ or close, really that light.This and other sources I have seen claim 0.27g/cm3https://solarsystem.nasa.gov/docs/13_Stackpoole-Poster.pdf
The HRSI tile was composed of high purity silica fibers. Ninety percent of the volume of the tile was empty space, giving it a very low density (9 lb/cu ft or 140 kg/m3) making it light enough for spaceflight.
While RCC had the best heat protection characteristics, it was also much heavier than the silica tiles and FIB blankets, so it was limited to relatively small areas. In general the goal was to use the lightest weight insulation consistent with the required thermal protection. Weight per unit volume of each TPS type:RCC: 1986 kg/m³ (124 lb/ft³)LI-2200 tiles: 352 kg/m³ (22 lb/ft³)FRCI tiles: 192 kg/m³ (12 lb/ft³)LI-900 (black or white) tiles: 144 kg/m³ (9 lb/ft³)FIB blankets: 144 kg/m³ (9 lb/ft³)
Here's what I have....https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=36039.0;attach=621091;sess=43050QuotePICA-X heat shield material boasts a density of only 0.27 g/ cm3, near the density of solid cork (0.24 g/cm3) [22]. The material needs only be a few centimeters thick (typically around 6 cm)
PICA-X heat shield material boasts a density of only 0.27 g/ cm3, near the density of solid cork (0.24 g/cm3) [22]. The material needs only be a few centimeters thick (typically around 6 cm)
Quote from: guckyfan on 04/13/2017 08:00 amQuote from: CharlieWildman on 04/13/2017 04:32 amCG with out nose weight looks quite scary to this untrained eye. Adding 5 tons of nose weight gets it looking possible. Maybe it wont take 5 tons. Maybe just 3 tons... But still... Yikes!To me it looks better than expected. Instead of ballast at the top drag devices at the back will be much lighter and get it stable as well. Drag and steering plates folding out at the bottom are quite simple and lightweight. They need to be covered with PicaX heatshields.Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh. Is PicaX density known? Couldn't find it searching the web.