The craft will hit the top of the atmosphere at a speed of 5.7 kilometers per second (12,750 miles per hour). Within the next six and a half minutes, it will use heat-generating atmospheric friction, then a parachute, then firings of descent thrusters, to bring that velocity down to about 2.4 meters per second (5.4 miles per hour) just before touchdown.
There is no guarantee of a successful landing, despite extensive analysis, testing and review of the entry, descent and landing system.
About 75 seconds after the parachute opens and 140 seconds before landing, the spacecraft will start using its radar. The radar will provide information to the onboard computer about distance to the ground, speed of descent and horizontal velocity. It will take readings at a pace of 10 times per second until touchdown.
Descent speed will have slowed to about 56 meters per second (125 miles per hour) by the time the lander separates from the back shell and parachute, about a kilometer (six-tenths of a mile) above the ground. The spacecraft will be in free fall, but not for long. Thrusters will begin firing half a second later and will increase their thrust three seconds after Phoenix sets itself free from the parachute. Touchdown will still be about 40 seconds away. The onboard computer will use information from the radar to adjust the pulsed firings of the 12 descent thrusters.
By the time the lander gets to about 30 meters (98 feet) above the surface, it will have slowed to about 2.4 meters per second (5.4 miles per hour) in vertical velocity. Continuous adjustments to the thruster firings based on radar sensing will also have minimized horizontal velocity and rocking. Touchdown will be about 12 seconds away.
ouch if the thrusters to slow the ship do not work as you will find mars in less than 20 sec....
Twelve thrusters mounted around the bottom edge of the lander will slow the descent during the last half-minute before the legs touch the surface. These can each pulse on and off for fine-tuning the velocity and for maintaining the lander’s stability -- controlling its pitch, yaw and roll -- as it approaches touchdown. They each provide about 293 newtons (65.9 pounds) of thrust.
https://en.wikipedia.org/wiki/Phoenix_(spacecraft)
Launch mass 670 kg 1,477 lb)
landing Mass 350 kg (770 lb)
eight 1.0 lbf (4.4 N) and 5.0 lbf (22 N) monopropellant hydrazine engines built by Aerojet-Redmond
https://mars.nasa.gov/insight/timeline/ … t-landing/
Compared with Phoenix, though, InSight's landing presented four added challenges:
InSight entered the atmosphere at a lower velocity -- 12,300 miles per hour (5.5 kilometers per second) vs. 12,500 miles per hour (5.6 kilometers per second).
InSight had more mass entering the atmosphere -- about 1,340 pounds (608 kilograms) vs. 1,263 pounds (573 kilograms).
InSight landed at an elevation of about 4,900 feet (1.5 kilometers) higher than Phoenix did, so it had less atmosphere to use for deceleration.
https://www.jpl.nasa.gov/news/press_kits/insight/
]]>https://en.wikipedia.org/wiki/Mars_Scie … ding_(EDL)
The mass of this EDM system, including parachute, sky crane, fuel and aeroshell, is 2,401 kg (5,293 lb).
The descent stage is a platform above the rover with eight variable thrust monopropellant hydrazine rocket thrusters on arms extending around this platform to slow the descent. Each rocket thruster, called a Mars Lander Engine (MLE), produces 400 to 3,100 N (90 to 697 lbf) of thrust and were derived from those used on the Viking landers.
I think you see where I am going with the scability towards what the dragon and larger as a means to prove we are on the correct path.
More launch details
https://www.jpl.nasa.gov/news/press_kits/MSLLaunch.pdf
Mars Science Laboratory: Entry, Descent, and Landing System Performance
https://ntrs.nasa.gov/archive/nasa/casi … 007730.pdf
Just hoping to fill in details for scaling for any shape that we would land on mars
Same landing was used by MSL
]]>GW
]]>My ancient Hoerner "drag bible" has NASA wind tunnel data from 1961 with a Mercury capsule shape somewhere around Mach 3. It shows the effects they saw on drag due to the retropropulsion plume: a slight reduction in effective drag coefficient. Not a word about plume instability or the side forces that could induce.
The plume coming out of the rocket nozzle is moving at Mach 9 plus, depending upon the expansion ratio of the nozzle. The oncoming stream for an Earth entry (not at Mars!) can be faster than that, but the rocket plume exit plane pressure is far higher than local atmospheric pressures, so there is far more momentum in the exhaust plume than in the oncoming stream.
The rocket plume must shock down to subsonic (relative to the oncoming stream, before it can turn and go with that stream. That is where any plume instability can occur. Once shocked down, momentum is much smaller, which is why the plume instability effect is not large.
The EDL (entry, descent, and landing) dilemma is all about what happens if you keep using the same heat shields, ringsail chutes, and terminal retrorockets) as payload mass grows. It's not the chute, it's the hypersonic entry trajectory.
At higher ballistic coefficient (which grows with mass on a square cube effect), you reach Mach 2.5 (the max opening speed of a ringsail chute) at lower altitudes. That CANNOT be avoided.
At lower opening altitude, there is less time available for the chute to decelerate you from Mach 2.5 to high subsonic (the best it can do, by the way, on Mars).
As the mass grows, you very quickly reach a point (about a ton or so) at which you start hitting the ground still supersonic. Carried to a ridiculous extreme, you don't even have time to deploy and open the chute.
All that conundrum really says is "do something different".
Forget the chute and make the retrorockets much bigger, to shoulder the deceleration load about the time you come out of hypersonics about Mach 3-ish. Now you can land several tons.
The other piece of this puzzle is chute scaling. Bigger masses require bigger chutes. There is a limit to chute loading (mass/opened planform area) that is set by the ability to actually deploy and successfully open the thing. True here and on Mars, just different numbers. Chutes are infeasible under any circumstances (here and Mars) if the payload mass gets big enough. Again, it's a square cube scaling thing.
Now you know why Spacex did what it did with Falcon stages, proposed what it did for Crew and Red Dragon, and is developing for both stages of its BFR. Bigness drives you to retropropulsion as the most feasible landing means.
GW
]]>As you can see it had a huge by comparison descent stage to land versus the much smaller ascent. Keep in mind though it had to dock with the departure stage that was parked in orbit for the means to return home.
You will see these same sizings of stages even in the current Altair - Lunar Lander (LSAM) - status thread in this folder.
Mars will be no different in those respects.
I did quite a bit of document gathering for the landing issues for mars and posted then under the MarsDrive (Human) Mission Design in response to Michael Bloxham needs and noted that other threads existed for a mission discussion on other forums lower down on that page for alternative mission designing.
As you noted it is not a desire to land with the return fuel so you would leave that in orbit and the ascent is a question of size of the insitu processing mass that needs to be landed in order to refuel as a source of hydrogen is needed for it to happen.
]]>You say:
"Also do not forget, that 1MT must also include the fuel tanks for the fuel too. Overall, powered breaking isn't out of the question, but if you are going to do that and bring the fuel you need for the trip back to Earth, forget about chemical rockets. Nuclear rockets on the other hand could pull it off perhaps."
That suggests you have an idea about how much fuel or overall rocket mass would be required to get 10 MT to Mars and back. Are you able to give the figure. I was thinking perhaps we were talking about 2,000 MT but are you saying it is much higher. If you're not why are you saying we should "forget it"?
]]>Oh and because of the thin Martian atmosphere, a big heat shield is probably preferred, unless your vehicle has a relatively low density.
And last, Lunar refueling is a bad idea, because it takes about as much fuel to get to the Moon then just to go to Mars directly.
]]>I'm a Mars Minimalist I think we can get there and establish permanent human settlement on a very small payload - but we have to change our way of thinking about the problem.
I'm also a retro rocket enthusiast.
So I;m suggesting a much smaller payload than some others do.
I think for Mission 1 we could go with two robot pre-flights delivering 10 tonnes each followed by two companion manned flights and landings of 10 tonnes each. So 40 tonnes total of which maybe 24 tonnes would be deployed following landing.
So do you have any thoughts on how big a single stage craft launched from earth using only retro rocket landing would have to be for a 10 tonne payload. Would something like 2000 tonnes be about right? Or is that too low?
Another way of addressing the problem once we had a lunar base would of course be to have the craft launch from earth with fuel tanks half or third empty, to refuel on the moon from lunar fuel. That seems like a very sensible way of proceeding to me.
]]>Yes the amount of energy is about the same as is required to escape Mars gravity. Low Mars orbit is about 4 kms/sec, and it's just possible to burn off the extra 1 kms/sec with current technology. For heavier payloads aerobraking has to be used, as was done with MRO. It's still not clear how a MD size payload (about 10 MT) can be safely landed on the surface.
]]>