SpaceX Tuesday...

SpaceX Tuesday...

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Discussion

Eric Mc

114,749 posts

229 months

Monday 5th January 2015
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Toaster said:
I don't disagree regarding the parachutes, but its been done before with the LEM in the 60's from around 61nm (from Mach 4.8 to 0 knots) and other landing craft such as mars curiosity rover although the latter did have a heat shield and parachute.

The question is how practical is this you use one shed load of fuel to launch and a heap more to slow it down.
The big difference in landing on the moon - and even Mars, is the lack of atmosphere and lower gravity fields. A powered descent to a hard surface is a lot easier in those circumstances.
And of course, parachutes are impossible in a vacuum.

The other factor is precision.

When landing on another planet it is not a big problem if you are a few miles out from your intended landing point. As long as you are within the landing ellipse you will be OK. That obviously is not the case on earth when trying to land at a very specific spot on terra firma.

MartG

17,635 posts

168 months

Monday 5th January 2015
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Eric Mc said:
When landing on another planet it is not a big problem if you are a few miles out from your intended landing point. As long as you are within the landing ellipse you will be OK. That obviously is not the case on earth when trying to land at a very specific spot on terra firma.
Or on a small barge in a big ocean

Toaster

2,881 posts

157 months

Monday 5th January 2015
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Eric Mc said:
The big difference in landing on the moon - and even Mars, is the lack of atmosphere and lower gravity fields. A powered descent to a hard surface is a lot easier in those circumstances.
And of course, parachutes are impossible in a vacuum.

The other factor is precision.

When landing on another planet it is not a big problem if you are a few miles out from your intended landing point. As long as you are within the landing ellipse you will be OK. That obviously is not the case on earth when trying to land at a very specific spot on terra firma.
Mars has an atmosphere, hence parachutes and a heatshield and Neil Armstrong landed the LEM with great accuracy he placed the LEM at a point of his choosing (after skipping over obstacles).

Whilst a body such as the moon may have less gravitational pull then the craft requires proportionally less fuel and smaller engine but it doesn't make it easier

Even the average amateur quad copter has GPS and can return to base with ease

Now the point of space X is a reliable, reusable rocket if the guys do it then great, it will be interesting to see the ratio of success/failures as time goes on

An interesting article http://www.universetoday.com/117873/nasa-mars-land...

Eric Mc

114,749 posts

229 months

Monday 5th January 2015
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Toaster said:
Mars has an atmosphere, hence parachutes and a heatshield and Neil Armstrong landed the LEM with great accuracy he placed the LEM at a point of his choosing (after skipping over obstacles).

Whilst a body such as the moon may have less gravitational pull then the craft requires proportionally less fuel and smaller engine but it doesn't make it easier

Even the average amateur quad copter has GPS and can return to base with ease

Now the point of space X is a reliable, reusable rocket if the guys do it then great, it will be interesting to see the ratio of success/failures as time goes on

An interesting article http://www.universetoday.com/117873/nasa-mars-land...
Mars has an extremely tenuous atmosphere - equal to an altitude of over 100,000 feet on earth. Chutes do work - for a bit - mainly to get the landing craft to subsonic speeds. but landing rockets are still usually required.

Apollo 11 missed its designated landing target by about 6 miles - because they hadn't factored in the propulsive force of residual air in the docking tunnel when they undocked from the Command Module prior to landing.
Later Apollos took this into account and landed very accurately - but they had humans on board to refine the approach using visual cues.
Even today automatically controlled landers are designed to come down within a "margin of error" ellipse.

And I would argue that a lower gravitational field and less of an atmosphere makes a rocket controlled landing IMMEASURABLY easier precisely BECAUSE the weight and fuel requirements are so much less. Aerodynamic factors can also be ignored when coming down in a vacuum.

I'm looking forward to this test and I really hope it works - eventually.


Caruso

7,142 posts

220 months

Monday 5th January 2015
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One difficulty with Mars is the variability of the atmosphere. The density can vary by a factor of 100% which means you've got a large margin of error in any Entry/Descent/Landing plan that uses the atmosphere to scrub off speed. The other factor as mentioned is that the atmosphere is very tenuous, limiting the weight of anything you can land by parachutes before the parachutes become most of the weight of the lander.

Each body in the solar system has it's own challenges for Entry/Descent/Landing. Earth's are probably the easiest to predict.

Toaster

2,881 posts

157 months

Monday 5th January 2015
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Eric Mc said:
Mars has an extremely tenuous atmosphere - equal to an altitude of over 100,000 feet on earth. Chutes do work - for a bit - mainly to get the landing craft to subsonic speeds. but landing rockets are still usually required.

Apollo 11 missed its designated landing target by about 6 miles - because they hadn't factored in the propulsive force of residual air in the docking tunnel when they undocked from the Command Module prior to landing.
Later Apollos took this into account and landed very accurately - but they had humans on board to refine the approach using visual cues.
Even today automatically controlled landers are designed to come down within a "margin of error" ellipse.

And I would argue that a lower gravitational field and less of an atmosphere makes a rocket controlled landing IMMEASURABLY easier precisely BECAUSE the weight and fuel requirements are so much less. Aerodynamic factors can also be ignored when coming down in a vacuum.

I'm looking forward to this test and I really hope it works - eventually.
But Mars still has an atmosphere, curiosity still used a heatshield, parachute and landing rockets and usually does not mean always.......

As for Apollo, it still was a remarkable achievement and all landed safely even space X if successful will land within 'a margin of error'

less of an atmosphere, gravity or even vacuum means that different calculations are required for a successful landing that does not make it immeasurably easier, its all hard.

Eric Mc

114,749 posts

229 months

Monday 5th January 2015
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The term "Easier" is relative. It doesn't mean it's "easy".

If they pull it off, I will be very impressed.

annodomini2

6,107 posts

215 months

Monday 5th January 2015
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Great achievement when they pull it off.

The real issue won't be the rocket, but the weather, high winds and/or rough seas are going to have a greater impact on it's possibility of success.

Eric Mc

114,749 posts

229 months

Monday 5th January 2015
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Eric Mc

114,749 posts

229 months

Monday 5th January 2015
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Very enjoyable presentation by the SpaceX chap. he said he's going to be "super-excited - if it works".

Salgar

3,282 posts

148 months

Tuesday 6th January 2015
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What time is this today?

Eric Mc

114,749 posts

229 months

Tuesday 6th January 2015
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Live coverage from 11.00 am on NASA TV or Spaceflightnow.

Eric Mc

114,749 posts

229 months

Tuesday 6th January 2015
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The weather - which was looking a bit iffy a few days ago, is now being shown as "90% favourable" for launch.

MrCarPark

528 posts

105 months

Tuesday 6th January 2015
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Eric Mc said:
Apollo 11 missed its designated landing target by about 6 miles - because they hadn't factored in the propulsive force of residual air in the docking tunnel when they undocked from the Command Module prior to landing.
Never knew that smile

Eric Mc

114,749 posts

229 months

Tuesday 6th January 2015
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Yes - Armstrong couldn't recognise a thing when the Lunar Module pitched over prior to landing.

Most of the descent from orbit was carried out with the Lunar Module facing upwards, away from the moon. This was so the landing radar, which was attached to the underside of the Descent Stage, could get good "pings" off the lunar surface as they got closer. The Pitchover Manoeuver was carried out at an altitude of about 1,000 feet altitude so they couldn't see where they were actually landing until quite late in the proceedings.

When "Eagle" pitched over, Armstrong got his first view of the landing site out the window and realised they were no where near they should have been. That's one of the reasons why he took over manual control and hovered for a bit whilst he sought out a safe spot to put down.

During the whole of their stay on the surface, no one knew exactly where they were. Michael Collins tried to find them visually from orbit using "Columbia's" 27 x sextant/telescope but he never did - because he was looking in the wrong place.

Later missions were pretty much pin point accurate and on a few occasions the LM was spotted on the surface by the Command Module Pilot because he knew the precise location each time.

Eric Mc

114,749 posts

229 months

Tuesday 6th January 2015
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Simpo Two

74,929 posts

229 months

Tuesday 6th January 2015
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Blast-off at 11.20am according to the commentary.

Eric Mc

114,749 posts

229 months

Tuesday 6th January 2015
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Hold Hold Hold

Engine start aborted - for the moment.

MartG

17,635 posts

168 months

Tuesday 6th January 2015
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Bugger frown


MartG

17,635 posts

168 months

Tuesday 6th January 2015
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Try again on Friday I guess