China's Space Program News Thread

[Engineer]

The thing is round trip timing of radio signals from moon to earth and back is only 2 seconds. There is no ionization blackout during lunar descent because the moon has no atmosphere, so the lander can remain in continuous contact with mission control all the way down to the surface, so it is possible for the lander to beam the picture back to earth and have decision beamed back in time to adjust its landing site.

No.

Firstly, the latency is just too much. If you don't believe me, try landing a plane in a flight simulator with 2 seconds lag. Secondly, communication link does not always work. If for one second you need the link and the link is not available, the mission would be over. No sane engineer would take that chance.

 

[Engineer]

I recall the lander was reported to be tested in Beijing but the report never said how lunar gravity could be simulated in the testing.

I think it is typically done by hardware-in-the-loop and distributed simulation.

Before the lander is assembled, all the components are connected to each other via a network. The physical rocket motors are also connected to the network from another facility, and with sensors attached to measure the thrust produced by the motors. Once everything is set up, a computer simulation is set in motion which fools the components into thinking it is the real deal. Together, the components give commands to the motors. The motors are fired, and the measurements from the motors are sent back into the simulation to adjust the simulated lander. The process repeats, until the simulated lander touches down.

Once the lander is assembled, the same test is done again, but minus the physical firing of the motors. Measurements from the rocket motors are instead replaced by outputs from another computer simulation.

 

[blacklist]

No.

Firstly, the latency is just too much. If you don't believe me, try landing a plane in a flight simulator with 2 seconds lag. Secondly, communication link does not always work. If for one second you need the link and the link is not available, the mission would be over. No sane engineer would take that chance.

moral of the story... in a split second decision, we don't have 2 second to spare

 

[chuck731]

I recall the lander was reported to be tested in Beijing but the report never said how lunar gravity could be simulated in the testing.

No lander or rover meant for another celestial body has ever needed to be tested on earth in its entirety under simulated extraterrestrial gravity. Static forces imposed by a gravity field relatively easy to account for in any engineering design.

 

[chuck731]

No.

Firstly, the latency is just too much. If you don't believe me, try landing a plane in a flight simulator with 2 seconds lag. Secondly, communication link does not always work. If for one second you need the link and the link is not available, the mission would be over. No sane engineer would take that chance.

I am not talking about remotely flying of the lander via detailed control instructions. I am talking about remotely analyzing the images of the proposed landing area and transmitting a site selection to an otherwise largely autonomous lander.

 

[TerraN_EmpirE]

No lander or rover meant for another celestial body has ever needed to be tested on earth under simulated extraterrestrial gravity. Static forces imposed by a gravity field is easy to account for in any engineering design.

the extremes are almost impossible to simulate. best we can do is test life span. have it cruise around the Gobi for a while.

 

[Engineer]

I am not talking about remotely flying of the lander via detailed control instructions. I am talking about remotely analyzing the images of the proposed landing area and transmitting a site selection to an otherwise largely autonomous lander.

My answer will still be the same in such case, word-for-word.

 

[chuck731]

Then the answer based on the reaction latency would be unfounded, if the lander has significant amount of hover time, say 30 seconds to 1 minute.

 

[chuck731]

the extremes are almost impossible to simulate. best we can do is test life span. have it cruise around the Gobi for a while.

Gobi is nowhere near as extreme as the moon, in terms of high and low temperature, hard radiation, and the amount of highly abrasive extremely fine particles that can become electromagnetically attached to equipment.

Other than Venus, the moon has the harshest environment of any place humans have soft landed equipment on.

 

[Quickie]

I think it is typically done by hardware-in-the-loop and distributed simulation.

Before the lander is assembled, all the components are connected to each other via a network. The physical rocket motors are also connected to the network from another facility, and with sensors attached to measure the thrust produced by the motors. Once everything is set up, a computer simulation is set in motion which fools the components into thinking it is the real deal. Together, the components give commands to the motors. The motors are fired, and the measurements from the motors are sent back into the simulation to adjust the simulated lander. The process repeats, until the simulated lander touches down.

Once the lander is assembled, the same test is done again, but minus the physical firing of the motors. Measurements from the rocket motors are instead replaced by outputs from another computer simulation.

No lander or rover meant for another celestial body has ever needed to be tested on earth in its entirety under simulated extraterrestrial gravity. Static forces imposed by a gravity field relatively easy to account for in any engineering design.

The testing conditions on earth are actually very different from the conditions during the actual landing of the probe on the moon. First of all you have a much less gravity force, 1/6 of earth's, acting on the lander/rover on the moon. This is a big difference, about 6 times less, from that of the earth's during the earth base testing of the vehicle. Reducing the mass of the vehicle won't do, because this wouldn't be actually simulating the actual mass of the vehicle on the moon, which is very important since the complex interaction of forces, including those inertia forces due to the mass of the vehicle, have to be taken into account during the landing.