Discussion
I thought it was interesting that the satellites were instructed to ditch BEFORE all the info has been analysed.
From the article it appears the scientists have not fully sifted through the data yet, so to my mind it would be more conservative to leave them in orbit until the data HAD been analysed in case there were anomalies which were to be investigated. But the NASA guys know much more than me, obv, so I'm sure there's a good reason to do what they did. Would be interesting to know what it was. Could be as simple as they were out of fuel so this was the latest they could leave it and still have a controlled ditching.
From the article it appears the scientists have not fully sifted through the data yet, so to my mind it would be more conservative to leave them in orbit until the data HAD been analysed in case there were anomalies which were to be investigated. But the NASA guys know much more than me, obv, so I'm sure there's a good reason to do what they did. Would be interesting to know what it was. Could be as simple as they were out of fuel so this was the latest they could leave it and still have a controlled ditching.
Simpo Two said:
DonnyMac said:
This was the reason combined with uncertainty that they may hit the historical Apollo sites in an uncontrolled descent (crash).
Given the percentage of the Moon occupied with Apollo landing sites I think that's rubbish. They couldn't hit one if they wanted to.Also, they weren't certain how much fuel was left in the tanks - by burning it all off it allowed the team to check how much was left in compared to how much they thought was left in. They can now use this info in future missions.
Emily Lakdawalla's blog is useful to read up on this kind of thing -
http://www.planetary.org/blogs/emily-lakdawalla/20...
Emily Lakdawalla's blog is useful to read up on this kind of thing -
http://www.planetary.org/blogs/emily-lakdawalla/20...
FunkyNige said:
Also, they weren't certain how much fuel was left in the tanks - by burning it all off it allowed the team to check how much was left in compared to how much they thought was left in. They can now use this info in future missions.
An F1 team knows how much fuel is in its tanks down to the last cm3. Why doesn't NASA?It seems very 'belt and braces' to me, logic more befitting the 1960s.
Simpo Two said:
FunkyNige said:
Also, they weren't certain how much fuel was left in the tanks - by burning it all off it allowed the team to check how much was left in compared to how much they thought was left in. They can now use this info in future missions.
An F1 team knows how much fuel is in its tanks down to the last cm3. Why doesn't NASA?It seems very 'belt and braces' to me, logic more befitting the 1960s.
Besides which, you're kind of missing the point. Even if they thought they knew how much was left, by burning it all they can check to see how far out their estimate was. That's the real point; they didn't have 'no idea' they had an idea they wanted to corroborate/recalibrate.
Simpo Two said:
FunkyNige said:
Also, they weren't certain how much fuel was left in the tanks - by burning it all off it allowed the team to check how much was left in compared to how much they thought was left in. They can now use this info in future missions.
An F1 team knows how much fuel is in its tanks down to the last cm3. Why doesn't NASA?It seems very 'belt and braces' to me, logic more befitting the 1960s.
"Fuel consumption models are necessary because no one has invented an entirely reliable fuel gauge for spacecraft. Until that day arrives, mission planners can approximate fuel usage by looking at the history of the vehicle's flight and how many times and for how long its rocket motors have fired."
FunkyNige said:
NASA say
"Fuel consumption models are necessary because no one has invented an entirely reliable fuel gauge for spacecraft. Until that day arrives, mission planners can approximate fuel usage by looking at the history of the vehicle's flight and how many times and for how long its rocket motors have fired."
Why not have a metal box, with a collapsible bag inside and a spring loaded plunger forming one end of the box?"Fuel consumption models are necessary because no one has invented an entirely reliable fuel gauge for spacecraft. Until that day arrives, mission planners can approximate fuel usage by looking at the history of the vehicle's flight and how many times and for how long its rocket motors have fired."
Plunger depth in = fuel used/remaining?
Easy.
I should work for NASA, me.
Fuels used in rockets are a lot more unstable compared to simple fuel like petrol. They are also in a very harsh environment where heating and pressure and temperature variations can cause the fuel to vapourise and vent - or even freeze.
NASA has a history of deliberately crashing used rocket and used moon probes onto the surface in a predetermined way to ensure that no existing equipment on the lunar surface is damaged. Back in the Apollo days, the ascent stages of the Lunar Module were deliberately crashed into areas where there no man made objects sitting on the surface.
The moon is actually peppered with dozens of man made objects - over and above the Apollo landing sites.
NASA has a history of deliberately crashing used rocket and used moon probes onto the surface in a predetermined way to ensure that no existing equipment on the lunar surface is damaged. Back in the Apollo days, the ascent stages of the Lunar Module were deliberately crashed into areas where there no man made objects sitting on the surface.
The moon is actually peppered with dozens of man made objects - over and above the Apollo landing sites.
Piersman2 said:
FunkyNige said:
NASA say
"Fuel consumption models are necessary because no one has invented an entirely reliable fuel gauge for spacecraft. Until that day arrives, mission planners can approximate fuel usage by looking at the history of the vehicle's flight and how many times and for how long its rocket motors have fired."
Why not have a metal box, with a collapsible bag inside and a spring loaded plunger forming one end of the box?"Fuel consumption models are necessary because no one has invented an entirely reliable fuel gauge for spacecraft. Until that day arrives, mission planners can approximate fuel usage by looking at the history of the vehicle's flight and how many times and for how long its rocket motors have fired."
Plunger depth in = fuel used/remaining?
Easy.
I should work for NASA, me.
mrmr96 said:
I thought it was interesting that the satellites were instructed to ditch BEFORE all the info has been analysed.
Fairly common this. SO much data is generated that it will be several years before it has been full analysed, and you can't keep experiments or spacecraft going for that long. They'll be satisfied that they've captured all of the data that they're going to get, and will have analysed some of it to confirm that the data is "good".Bedazzled said:
I guess ditching is better than creating a dyson sphere of dangerous junk in orbit. Pity they couldn't reduce the impact speed a bit more; 3,700mph after a 5 min burn presumably against the direction of travel... engines can't have been very powerful, what speed were they doing while in orbit?
Not much more than 3,700 mph.The speed required to maintain orbit of around 60 miles above the moons surface does not need to be much above 4,000 mph relative to the moon.
To slow an object down to such an extent that it can land softly on the moon requires quite a bit a fuel - far more than would have been on these relatively small spacecraft.
Bedazzled said:
I guess even a few molecules of trace atmosphere must add drag when they are close to the surface, or maybe it's gravitational effects?
IIRC the moon has a very 'lumpy' gravitational field due to mass concentrations at various places - this tends to perturb any orbit over a fairly short period of time.Looking at comments elsewhere about these probes being ditched, it's appaling the level of ignorance being displayed with people complaining that NASA are littering the moon and destroying its landscape - FFS it gets hit by bigger and faster meteorites on a regular basis, and it would take a hell of a lot of litter to be noticeable on a land area similar to the continent of Africa !
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