Author Topic: Israeli robotic lunar lander  (Read 2121 times)

Offline bknight

  • Neptune
  • ****
  • Posts: 2746
Israeli robotic lunar lander
« 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)
Truth needs no defense.  Nobody can take those footsteps I made on the surface of the moon away from me.
Eugene Cernan

Offline onebigmonkey

  • Saturn
  • ****
  • Posts: 1327
  • ALSJ Clown
    • Apollo Hoax Debunked
Re: Israeli robotic lunar lander
« Reply #1 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.

Offline Von_Smith

  • Venus
  • **
  • Posts: 37
Re: Israeli robotic lunar lander
« Reply #2 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?"

Offline raven

  • Saturn
  • ****
  • Posts: 1428
Re: Israeli robotic lunar lander
« Reply #3 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.

Offline bknight

  • Neptune
  • ****
  • Posts: 2746
Re: Israeli robotic lunar lander
« Reply #4 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.  :)
Truth needs no defense.  Nobody can take those footsteps I made on the surface of the moon away from me.
Eugene Cernan

Offline raven

  • Saturn
  • ****
  • Posts: 1428
Re: Israeli robotic lunar lander
« Reply #5 on: February 22, 2019, 01:54:15 AM »
Seriously though, I wish them all the best with this endeavour. No easy task this.

Offline Peter B

  • Jupiter
  • ***
  • Posts: 825
Re: Israeli robotic lunar lander
« Reply #6 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)

Offline bknight

  • Neptune
  • ****
  • Posts: 2746
Re: Israeli robotic lunar lander
« Reply #7 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
Truth needs no defense.  Nobody can take those footsteps I made on the surface of the moon away from me.
Eugene Cernan

Online JayUtah

  • Neptune
  • ****
  • Posts: 3032
    • Clavius
Re: Israeli robotic lunar lander
« Reply #8 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.
"Facts are stubborn things." --John Adams

Offline raven

  • Saturn
  • ****
  • Posts: 1428
Re: Israeli robotic lunar lander
« Reply #9 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.

Offline Peter B

  • Jupiter
  • ***
  • Posts: 825
Re: Israeli robotic lunar lander
« Reply #10 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?

Offline cjameshuff

  • Mars
  • ***
  • Posts: 333
Re: Israeli robotic lunar lander
« Reply #11 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), 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) which may have reduced its capability to handle long burns.

Online JayUtah

  • Neptune
  • ****
  • Posts: 3032
    • Clavius
Re: Israeli robotic lunar lander
« Reply #12 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.
"Facts are stubborn things." --John Adams

Offline bknight

  • Neptune
  • ****
  • Posts: 2746
Re: Israeli robotic lunar lander
« Reply #13 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.
« Last Edit: February 24, 2019, 12:15:22 PM by bknight »
Truth needs no defense.  Nobody can take those footsteps I made on the surface of the moon away from me.
Eugene Cernan

Offline molesworth

  • Earth
  • ***
  • Posts: 188
  • the curse of st custards
Re: Israeli robotic lunar lander
« Reply #14 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.
Days spent at sea are not deducted from one's allotted span - Phoenician proverb