Live stream of lunar landing tonight

[odysseus2000]

Maybe future lunar landers need to have a "this way up" on the side just so people can tell which way it is oriented?

Despite clear instructions, that didn't prevent a technician installing accelerometers upside down on a Russian Proton-M - which crashed as a consequence:

...a report from Russian Space Web says investigators have traced the problem to a series of sensors that were apparently installed upside down.

The so-called angular velocity sensors (дачик угловой скорости in Russian, according to NPR's Moscow bureau) were a critical part of the circuitry that kept the rocket upright during launch. They were so important, says Russian Space Web, that they even had little arrows on them that were supposed to point toward the top of the rocket.

Quite a spectacular video here:

https://www.npr.org/sections/thetwo-way/2013/07/10/200775748/report-upside-down-sensors-toppled-russian-rocket

RC

I once listened to an air investigator describing a plane crash. From the wreckage they found that someone had ground off the guide pins on a fuel valve that prevented incorrect orientation allowing the valve to be put in the wrong way.

Someone once said that fools are ingenious as in this case, but in many cases it is designs that do not make incorrect orientation impossible without tampering with the device. Recently I blew up a cnc mill controller by mistakenly connecting a male barrel connector to the wrong female receptacle. After that I taped up the wrong receptacle on the new board but my inattention & ease of screwing up cost me over a week & money to recover from. Sometimes troubles come very unexpectedly due to events beyond control. Last week I got a mains shock thanks to something (mouse?) having broken the insulation on a mains cable leaving bare copper exposed that had oxidized to be difficult to see against the black pvc cable. It always makes sense to eye over things before & during use & where possible have check lists to ensure things are not forgotten.

Regards,

[9873210]

It is strange that they don’t retro out the horizontal velocity to give a pure vertical decent, but perhaps the horizontal velocity is needed in case it spots something in the way of landing.

Regards,

It's more fuel efficient for every burn to make some contribution to zeroing both components. This follows from the small angle approximations. If you take that to the logical extreme, you only hit zero horizontal velocity as you contact the ground.

The preference for zeroing out one component then the other is usually a concession to people not being able to do two things at once. If there's no man in the loop no such simplification is needed.

(The above is true if you need some sort of terminal guidance. If you have perfect control the optimal landing is entirely horizontal, from a grazing orbit that reaches almost zero height and zero vertical velocity before you start the landing burn.)

[odysseus2000]

It is strange that they don’t retro out the horizontal velocity to give a pure vertical decent, but perhaps the horizontal velocity is needed in case it spots something in the way of landing.

Regards,

It's more fuel efficient for every burn to make some contribution to zeroing both components. This follows from the small angle approximations. If you take that to the logical extreme, you only hit zero horizontal velocity as you contact the ground.

The preference for zeroing out one component then the other is usually a concession to people not being able to do two things at once. If there's no man in the loop no such simplification is needed.

(The above is true if you need some sort of terminal guidance. If you have perfect control the optimal landing is entirely horizontal, from a grazing orbit that reaches almost zero height and zero vertical velocity before you start the landing burn.)

Presumably this kind of landing would be most suited to a flat surface like a still lake, but if you have undulating terrain with peaks & valleys would not a horizontal landing likely come to grief on some high object? Or am I misunderstanding what you say?

Regards,

[9873210]

It's more fuel efficient for every burn to make some contribution to zeroing both components. This follows from the small angle approximations. If you take that to the logical extreme, you only hit zero horizontal velocity as you contact the ground.

The preference for zeroing out one component then the other is usually a concession to people not being able to do two things at once. If there's no man in the loop no such simplification is needed.

(The above is true if you need some sort of terminal guidance. If you have perfect control the optimal landing is entirely horizontal, from a grazing orbit that reaches almost zero height and zero vertical velocity before you start the landing burn.)

Presumably this kind of landing would be most suited to a flat surface like a still lake, but if you have undulating terrain with peaks & valleys would not a horizontal landing likely come to grief on some high object? Or am I misunderstanding what you say?

Regards,

It sounds like you understand. You need to make sure there are no obstacles in the path and that the precision of your control is better than the undulations near your landing site. You don't need completely flat, you could try this onto a flat-topped mesa or even into an uphill slope, just don't land long! In practice I'd expect you would always need some terminal landing maneuver. Apollo's decent orbit had a perilune of 50,000 ft. A robotic probe with modern controls and willing to take more risk can use a decent orbit with a lower perilune. How much lower depends on your ground reconnaissance, spacecraft control, and the nerve/insanity of your steely eyed rocket men.

[odysseus2000]

Rather disappointing update:

https://youtu.be/oF3kF6RGFgM?si=Q9U9tY26wbtNHsAF

Regards,