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Off Topic => General Discussion => Topic started by: bknight on February 20, 2019, 02:30:56 PM

Title: Israeli robotic lunar lander
Post by: bknight on February 20, 2019, 02:30:56 PM
I can visualize the plethora of YT videos that they didn't find evidence of any Apollo landings.  Never mind that the lander may land several hundred to thousand of miles from any Apollo cite.

https://www.space.com/spacex-to-launch-israeli-moon-lander.html

Oh well, I think it if good that research on the Lunar surface has grown in the last couple of months.  8)
Title: Re: Israeli robotic lunar lander
Post by: onebigmonkey on February 21, 2019, 11:53:46 AM
At least one web user I know at ATS is frothing at the mouth that there is Israeli government money involved so it can't be private, and, well, you know, Jews.
Title: Re: Israeli robotic lunar lander
Post by: Von_Smith on February 21, 2019, 05:54:00 PM
I can't possibly be the only person to have thought of "Does a Beresheet on the moon?"
Title: Re: Israeli robotic lunar lander
Post by: raven on February 21, 2019, 06:28:40 PM
I can't possibly be the only person to have thought of "Does a Beresheet on the moon?"
Since the moon has no woods, I doubt it.
Title: Re: Israeli robotic lunar lander
Post by: bknight on February 21, 2019, 10:35:57 PM
I can't possibly be the only person to have thought of "Does a Beresheet on the moon?"

It's a good thing I saw this tonight instead of in the morning with a mouthful of coffee.  :)
Title: Re: Israeli robotic lunar lander
Post by: raven on February 22, 2019, 01:54:15 AM
Seriously though, I wish them all the best with this endeavour. No easy task this.
Title: Re: Israeli robotic lunar lander
Post by: Peter B on February 22, 2019, 09:11:18 AM
I can't possibly be the only person to have thought of "Does a Beresheet on the moon?"

Well, actually, I was thinking of the song "Jews in Space" at the end of Mel Brooks's "History of the World Part 1" (https://en.wikipedia.org/wiki/History_of_the_World%2C_Part_I#Previews_of_coming_attractions)
Title: Re: Israeli robotic lunar lander
Post by: bknight on February 22, 2019, 10:04:30 AM
Interesting trajectory and Lunar capture prior to landing.

https://www.space.com/israel-lunar-lander-long-trip-moon.html
Title: Re: Israeli robotic lunar lander
Post by: JayUtah on February 22, 2019, 11:40:58 PM
It's similar to the SMART-1 trajectory.  They got to the Moon from Earth orbit on no more propellant than it takes to gas up a medium sized pickup truck.
Title: Re: Israeli robotic lunar lander
Post by: raven on February 23, 2019, 12:41:34 AM
It's similar to the SMART-1 trajectory.  They got to the Moon from Earth orbit on no more propellant than it takes to gas up a medium sized pickup truck.
SMART-1  used an ion engine of some sort though, I believe. I think Beresheet is using a storable bi-propellent rocket.
Title: Re: Israeli robotic lunar lander
Post by: Peter B on February 24, 2019, 03:33:23 AM
Interesting trajectory and Lunar capture prior to landing.

https://www.space.com/israel-lunar-lander-long-trip-moon.html

After so many missions to asteroids or other planets or the Sun that take years, the idea of a mission that can reach its objective in three days sometimes seems a bit unexpected - I remember people on another science forum (Dr Karl's Self Service Science IIRC) having that attitude with the LRO back in 2009.

So perhaps the Beresheet crew can promote their mission as: taking as long as you're used to.

= = = =

Incidentally, how is it that multiple short burns to raise the apogee are more efficient than a single longer one? Is it that the efficiency of the burn is greatest when the spacecraft is closest to perigee, and this efficiency drops off considerably even minutes either side of perigee?
Title: Re: Israeli robotic lunar lander
Post by: cjameshuff on February 24, 2019, 08:35:17 AM
Interesting trajectory and Lunar capture prior to landing.

https://www.space.com/israel-lunar-lander-long-trip-moon.html

After so many missions to asteroids or other planets or the Sun that take years, the idea of a mission that can reach its objective in three days sometimes seems a bit unexpected - I remember people on another science forum (Dr Karl's Self Service Science IIRC) having that attitude with the LRO back in 2009.

So perhaps the Beresheet crew can promote their mission as: taking as long as you're used to.

= = = =

Incidentally, how is it that multiple short burns to raise the apogee are more efficient than a single longer one? Is it that the efficiency of the burn is greatest when the spacecraft is closest to perigee, and this efficiency drops off considerably even minutes either side of perigee?

It's more than a few minutes, that single long burn could be in the area of half an hour.

It may also have more to do with thermal limits. The LEROS 2b is rated for continuous burns of over an hour (datasheet (https://www.moog.com/literature/Space_Defense/Spacecraft/Propulsion/Upper_Stage_Engines_Rev_0913.pdf)), but the rest of the vehicle might heat up too much. They've also modified the engine to shorten the nozzle and increase the thrust (Nammo press release (https://www.mynewsdesk.com/no/nammo/pressreleases/nammos-british-rocket-engine-powers-israels-mission-to-the-moon-2838630)) which may have reduced its capability to handle long burns.
Title: Re: Israeli robotic lunar lander
Post by: JayUtah on February 24, 2019, 11:53:51 AM
SMART-1  used an ion engine of some sort though, I believe. I think Beresheet is using a storable bi-propellent rocket.

Yes:  similar trajectory but different engine trajectory.  Except not really similar trajectory.  Just the principle that if you're willing to have patience, you can change the fuel parameters.

So perhaps the Beresheet crew can promote their mission as: taking as long as you're used to.

Or merely, "...an appropriate orbit for an unmanned spacecraft."  A low-energy orbit isn't practical for Apollo because you have other consumables to support human life that would have to be increased to sustain the crew for the longer mission.  There's a sweet spot between the required propellant mass and the required consumables mass.  Then you have probably-of-failure distributions for all the critical equipment.  The longer the mission, the longer the period over which you have to integrate that failure function -- that is, the higher the probability something critical will fail.  Again there's a sweet spot between the probability of failure by operating the spacecraft over a longer time and the probability of failure by employing a higher-energy propulsion system.

The trajectory here is closer to the cycler concept than the ever-accelerating SMART-1 orbit.  That comparison was pemature.  The operational advantage you get from cycling your way hither and yon is that you have a lot of opportunities to observe the developing orbit and adjust it efficiently with the main propulsion burns.  In contrast, Apollo required the MCC type burns, which are themselves the sweet spots between how accurately you can observe the orbit versus how efficiently you can alter it.  The design and planning portions of aerospace engineering are all about the sweet spots.

Quote
Incidentally, how is it that multiple short burns to raise the apogee are more efficient than a single longer one? Is it that the efficiency of the burn is greatest when the spacecraft is closest to perigee, and this efficiency drops off considerably even minutes either side of perigee?

Well, yes for certain concepts of "efficiency."  Adding kinetic energy to an elliptical orbit changes its shape.  How the shape changes depends on where in the orbit you add it -- the real anomaly of your spacecraft.  You know the circularization maneuver; it's applied at apogee, and it has the effect of raising the perigee.  At apogee, the spacecraft is at the right altitude but the "wrong" velocity.  The velocity is too slow for a circular orbit at that altitude, so you just add velocity while at that altitude.  Think of the Beeresheet orbit as the opposite -- it's an elongation maneuver.  If you add velocity at perigee, it changes the shape of the orbit by raising the apogee.  Or you can think of it as elongating the orbit, changing its eccentricity.  The highly-eccentric orbit is the lowest-energy orbit having the desired altitude at some point (instead of at many or all points).  It just takes several cycles to achieve with minimal fuel.

The goal here is to get to the Moon.  Or rather, to achieve the farthest distance from the Earth with the least effort.  This orbit achieves that by means of a long, skinny orbit whose apogee is at the desired altitude.  Once you reach an apogee altitude of 238,000 miles or so, it's just a matter of waiting for the Moon to come along and change the orbital mechanics from a two-body problem to a restricted three-body problem.

It may also have more to do with thermal limits.

I don't know if that's the reason here, but it's often the reason.  The point of the LM plume deflectors was to lengthen the duty cycle for thermal reasons.
Title: Re: Israeli robotic lunar lander
Post by: bknight on February 24, 2019, 12:06:57 PM
SMART-1  used an ion engine of some sort though, I believe. I think Beresheet is using a storable bi-propellent rocket.

Yes:  similar trajectory but different engine trajectory.  Except not really similar trajectory.  Just the principle that if you're willing to have patience, you can change the fuel parameters.

So perhaps the Beresheet crew can promote their mission as: taking as long as you're used to.

Or merely, "...an appropriate orbit for an unmanned spacecraft."  A low-energy orbit isn't practical for Apollo because you have other consumables to support human life that would have to be increased to sustain the crew for the longer mission.  There's a sweet spot between the required propellant mass and the required consumables mass.  Then you have probably-of-failure distributions for all the critical equipment.  The longer the mission, the longer the period over which you have to integrate that failure function -- that is, the higher the probability something critical will fail.  Again there's a sweet spot between the probability of failure by operating the spacecraft over a longer time and the probability of failure by employing a higher-energy propulsion system.

The trajectory here is closer to the cycler concept than the ever-accelerating SMART-1 orbit.  That comparison was pemature.  The operational advantage you get from cycling your way hither and yon is that you have a lot of opportunities to observe the developing orbit and adjust it efficiently with the main propulsion burns.  In contrast, Apollo required the MCC type burns, which are themselves the sweet spots between how accurately you can observe the orbit versus how efficiently you can alter it.  The design and planning portions of aerospace engineering are all about the sweet spots.

Quote
Incidentally, how is it that multiple short burns to raise the apogee are more efficient than a single longer one? Is it that the efficiency of the burn is greatest when the spacecraft is closest to perigee, and this efficiency drops off considerably even minutes either side of perigee?

Well, yes for certain concepts of "efficiency."  Adding kinetic energy to an elliptical orbit changes its shape.  How the shape changes depends on where in the orbit you add it -- the real anomaly of your spacecraft.  You know the circularization maneuver; it's applied at apogee, and it has the effect of raising the perigee.  At apogee, the spacecraft is at the right altitude but the "wrong" velocity.  The velocity is too slow for a circular orbit at that altitude, so you just add velocity while at that altitude.  Think of the Beeresheet orbit as the opposite -- it's an elongation maneuver.  If you add velocity at perigee, it changes the shape of the orbit by raising the apogee.  Or you can think of it as elongating the orbit, changing its eccentricity.  The highly-eccentric orbit is the lowest-energy orbit having the desired altitude at some point (instead of at many or all points).  It just takes several cycles to achieve with minimal fuel.

The goal here is to get to the Moon.  Or rather, to achieve the farthest distance from the Earth with the least effort.  This orbit achieves that by means of a long, skinny orbit whose apogee is at the desired altitude.  Once you reach an apogee altitude of 238,000 miles or so, it's just a matter of waiting for the Moon to come along and change the orbital mechanics from a two-body problem to a restricted three-body problem.
And then the gravity of the Moon has a chance of changing the orbit since it has greater influence than the Earth at that position?
Quote

It may also have more to do with thermal limits.

I don't know if that's the reason here, but it's often the reason.  The point of the LM plume deflectors was to lengthen the duty cycle for thermal reasons.

Nice elaboration for we that aren't rocket scientists.

ETA: I didn't see/hear whether they had a schedule of burns, but I supposed it would be burn wait for a set number of orbits to determine the exact change and then repeat the burn cycle.
Title: Re: Israeli robotic lunar lander
Post by: molesworth on February 24, 2019, 04:42:16 PM
Incidentally, how is it that multiple short burns to raise the apogee are more efficient than a single longer one? Is it that the efficiency of the burn is greatest when the spacecraft is closest to perigee, and this efficiency drops off considerably even minutes either side of perigee?
Isn't that known as the Oberth Manoeuvre?  You get more bang for your buck at high velocity than low.
Title: Re: Israeli robotic lunar lander
Post by: JayUtah on February 24, 2019, 04:52:27 PM
Isn't that known as the Oberth Manoeuvre?  You get more bang for your buck at high velocity than low.

Yep.
Title: Re: Israeli robotic lunar lander
Post by: ka9q on February 25, 2019, 06:20:34 PM
Incidentally, how is it that multiple short burns to raise the apogee are more efficient than a single longer one? Is it that the efficiency of the burn is greatest when the spacecraft is closest to perigee, and this efficiency drops off considerably even minutes either side of perigee?
This assumes an instantaneous burn. If the required burn time is too long, it might be more efficient to split it up to a bunch of shorter ones.
Title: Re: Israeli robotic lunar lander
Post by: ka9q on February 25, 2019, 06:24:57 PM
I haven't studied the Beresheet trajectory, but another consideration is that it is more efficient to do plane changes at apogee. If one is necessary along with apogee raising, it might be more efficient to establish an intermediate apogee to do the plane change.
Title: Re: Israeli robotic lunar lander
Post by: bknight on February 26, 2019, 12:26:49 PM
First burn was successful raising the perigee to 600 Km.

https://spacenews.com/spaceil-lunar-lander-makes-first-post-launch-maneuvers/
Title: Re: Israeli robotic lunar lander
Post by: bknight on March 01, 2019, 01:12:34 PM
A second burn successfully completed after a aborted attempt on Monday.  The new Apogee is 131000 Km.

https://www.space.com/israel-moon-lander-beresheet-engine-firing.html
Title: Re: Israeli robotic lunar lander
Post by: bknight on March 21, 2019, 07:42:14 AM
A final burn has been completed for the craft to enter an orbit of the Moon.

https://www.israelnationalnews.com/News/News.aspx/260690
Title: Re: Israeli robotic lunar lander
Post by: raven on March 21, 2019, 11:23:29 PM
A final burn has been completed for the craft to enter an orbit of the Moon.

https://www.israelnationalnews.com/News/News.aspx/260690
"Israel’s first spacecraft performed a special maneuver Wednesday night, aimed at putting the lunar lander into position to achieve a stable lunar orbit."
"Israel’s first spacecraft."
***
To quote Miss Clavel of Madeline fame, "Something is not right."
Title: Re: Israeli robotic lunar lander
Post by: ka9q on March 24, 2019, 01:33:48 PM
The article says it was a plane change. That's as I had expected, since a plane change is more efficient at a high apogee where the orbital velocity is lowest. They can be extremely expensive in low orbit.

Title: Re: Israeli robotic lunar lander
Post by: bknight on March 28, 2019, 08:35:14 AM
Beresheet Gears up for Lunar Rendezvous
Quote
As of Thursday, 28 March, Beresheet is making its final orbit around the Earth. On 30 March, it will hit perigee, buzz past its home planet one last time, and head towards the Moon, roughly 405,000 kilometers distant. SpaceIL senior engineer Yoav Landsman said the spacecraft will make a small trajectory correction on 1 April. The duration of the lunar insertion burn on 4 April, as well as the parameters of the initial lunar orbit, have yet to be decided, but SpaceIL was originally planning for an orbit roughly 10,000 by 300 kilometers. Landing won't happen for another week, on 11 April.

http://www.planetary.org/blogs/jason-davis/beresheet-gears-up-for-lunar.html
Title: Re: Israeli robotic lunar lander
Post by: Dalhousie on March 29, 2019, 05:10:54 PM
At least one web user I know at ATS is frothing at the mouth that there is Israeli government money involved so it can't be private, and, well, you know, Jews.

Since it is built by a company that is heavily underwritten by the Israeli government the hype about it being the first private missions is a bit excessive.
Title: Re: Israeli robotic lunar lander
Post by: bknight on April 04, 2019, 11:19:02 AM
From yesterday
Israel’s Beresheet lander arrives in lunar orbit

https://spaceflightnow.com/2019/04/03/israels-beresheet-lander-heads-for-make-or-break-maneuver-to-enter-lunar-orbit/

Landing attempt n the 11th still.

ETA:  LO, I realize that this is in the hoax forum, if you want to move it to an appropriate thread.
Title: Re: Israeli robotic lunar lander
Post by: JayUtah on April 04, 2019, 11:33:13 AM
ETA:  LO, I realize that this is in the hoax forum, if you want to move it to an appropriate thread.

I was going to ask about that.
Title: Re: Israeli robotic lunar lander
Post by: bknight on April 04, 2019, 12:17:11 PM
ETA:  LO, I realize that this is in the hoax forum, if you want to move it to an appropriate thread.

I was going to ask about that.

I freely and openly confess an error on my part in the OP.  :-[
Title: Re: Israeli robotic lunar lander
Post by: LunarOrbit on April 05, 2019, 09:00:43 AM
LO, I realize that this is in the hoax forum, if you want to move it to an appropriate thread.

No problem.
Title: Re: Israeli robotic lunar lander
Post by: bknight on April 06, 2019, 01:37:53 PM
Some images of the far side of the Moon.

https://www.space.com/israeli-lander-moon-far-side-photos.html?utm_source=sdc-newsletter&utm_medium=email&utm_campaign=20190406-sdc
Title: Re: Israeli robotic lunar lander
Post by: bknight on April 11, 2019, 02:11:56 PM
Landing attempt today at 1500-1600 EDT today.  Link to the live broadcast.

https://www.space.com/israel-moon-landing-beresheet-webcast.html?utm_source=sdc-newsletter&utm_medium=email&utm_campaign=20190411-sdc
Title: Re: Israeli robotic lunar lander
Post by: Zakalwe on April 11, 2019, 03:43:24 PM
Crashed, unfortunately.
The descent engine failed some 10 klicks up :-[
Title: Re: Israeli robotic lunar lander
Post by: bknight on April 11, 2019, 03:46:31 PM
Crashed, unfortunately.
The descent engine failed some 10 klicks up :-[

I was just coming on to post that, but you beat me to the punch.
Too bad for them, it would have been nice to have another lander for a short time.
Title: Re: Israeli robotic lunar lander
Post by: Apollo 957 on April 12, 2019, 05:08:29 AM
They grabbed (at least) a couple of good photos from orbit and descent before they lost comms, though.
Title: Re: Israeli robotic lunar lander
Post by: onebigmonkey on April 12, 2019, 08:46:26 AM
Shame it failed when it did as it was about to fly over the Apollo 11 site!

I watched the live feed of this and it was getting obvious to me that it wasn't going as planned - it still had an awful lot of velocity to shave off with not far to go!

I await the inevitable "Aliens did it" competing with "if we can't do it now with our modern technology home come..." amongst youtube's most learned.
Title: Re: Israeli robotic lunar lander
Post by: bknight on April 12, 2019, 11:48:51 AM
Shame it failed when it did as it was about to fly over the Apollo 11 site!

I watched the live feed of this and it was getting obvious to me that it wasn't going as planned - it still had an awful lot of velocity to shave off with not far to go!

I await the inevitable "Aliens did it" competing with "if we can't do it now with our modern technology home come..." amongst youtube's most learned.

Yes probably Mr. Strange or taffy  >:(
Title: Re: Israeli robotic lunar lander
Post by: ka9q on April 13, 2019, 03:05:22 AM
I just hope they get the chance to try again. It would be a shame to waste all that engineering work and experience on just one failed mission.
Title: Re: Israeli robotic lunar lander
Post by: bknight on April 13, 2019, 08:09:18 AM
I just hope they get the chance to try again. It would be a shame to waste all that engineering work and experience on just one failed mission.

They are going to try again
Quote
Israel may not have succeeded in a soft landing on the moon, but the tiny country is not giving up on its lunar ambitions just yet. Israeli Prime Minister Benjamin Netanyahu, who watched the landing attempt from the mission control room, said Israel will try to land on the moon again in the next two to three years.

https://www.space.com/beresheet-moon-crash-engine-glitch.html

Title: Re: Israeli robotic lunar lander
Post by: ka9q on April 13, 2019, 07:00:51 PM
Sounds somewhat like the Surveyor 4 failure, when contact was lost just a few minutes before landing. I don't think the cause was definitively found, but the explosion of the solid fuel retrorocket seemed the most likely cause.