Smart-1, To Crash Into Lunar Surface In August Options

[abalone]

What is the impact speed 1.5km/s? Probably more like a plane crash the a meteorite impact
http://www.spacedaily.com/reports/SMART_1_..._In_August.html

[paxdan]

What is the impact speed 1.5km/s?

Smart-1 impact: 1.5 km/s x 367 kg

Lunar Prospector impact: 1.7 km/s x 160 kg

lets hope for a better show this time

[AndyG]

Smart-1 impact: 1.5 km/s x 367 kg

Lunar Prospector impact:  1.7 km/s x 160 kg

lets hope for a better show this time

Hmmm...413 MJ...almost exactly 100kg of TNT equivalent. That said, it's only 80% more energy than Lunar Prospector. But then the reports suggest it's going to be visible (i.e. on the near side, and not all-but hidden in a polar crater?)

Andy G

[tty]

What is the impact speed 1.5km/s? Probably more like a plane crash the a meteorite impact
http://www.spacedaily.com/reports/SMART_1_..._In_August.html

Actually I think the speed of a lunar satellite close to the surface is about 1.7 kms-1, but even taking 1.5 kms-1 I would like to point out that this is about equal to Mach 5, which is a rather higher speed than an APDS shell has when leaving a tank gun. Hardly your typical plane crash which normally occurs at about a tenth of the speed and a hundredth of the kinetic energy per pound.

tty

[Toma B]

The crash, which will be observable by telescope from Earth...

I just hate that kind of reporting...
-There is no mention about what kind of telescope would be appropriate to watch that event...KECK or my "Orion" Newton 4,5" reflector short-tube telescope...
-Will SMART-1 hit illuminated or not illuminated side of visible side of the Moon?
-From what part of Earth will this be visible?
...is there any real report about this event?

[djellison]

I'd hope they do it on the dark side so that we can all get out our binos and watch for it.

Doug

[ljk4-1]

I'd hope they do it on the dark side so that we can all get out our binos and watch for it.

Doug

This reminded me of Robert Goddard's plan in 1920:

"to [send] to the dark part of the new moon a sufficiently amount of the most brilliant flash powder which, in being ignited on impact, would be plainly visible in a powerful telescope. This would be the only way of proving that the rocket had really left the attraction of the earth as the apparatus would never come back."

Quoted from here:

http://en.wikipedia.org/wiki/Robert_Goddard_%28scientist%29

Did Goddard say how much flash powder would be needed to make the flash visible from Earth? Would his plan have been possible?

Note: The 80th anniversary of Goddard launching the first liquid-fueled rocket is coming up on March 16:

http://en.wikipedia.org/wiki/Image:Goddard_and_Rocket.jpg

[abalone]

I'd hope they do it on the dark side so that we can all get out our binos and watch for it.

Doug

From the report, it gives the impression that they will be looking for a dust cloud. I dont think that 1.7km/s is fast enough to vaporise anything and I assume it is almost out of any chemical propellants that might result in an explosion.

For these reasoms the best impact conditions are probably just over the dark side of the terminator to make any small explosion visible and illuminate any rising dust cloud against the dark background

[Phil Stooke]

As things stand now the impact will be on the far side. If there is sufficient propellant left the orbit will be adjusted to make impact occur about 2 weeks earlier or later, so it will be on the near side. Since an exact position is not yet chosen (and depends on the fuel available) we can't say if it will be illuminated or not.

The only impact certainly known to have been seen from Earth was Hiten. Ranger and Apollo SIVB impacts were not seen, though efforts were made to see the Ranger impacts. But Luna 2, Luna 5 and Luna 7 impacts were reportedly seen or photographed. But most US astronomers discounted those reports. This would be a unique chance to assess the visibility of an impact using modern equipment.

The Hiten impact was seen in IR from Australia, just on the dark side of the terminator near Furnerius crater.

[RNeuhaus]

Then, I am afraid that the HSB space telescope is the only which can see the impact flash?

Rodolfo

[AndyG]

Did Goddard say how much flash powder would be needed to make the flash visible from Earth?  Would his plan have been possible?

Let's see - back of an enveloping:

The Sun shines at mag -26.7. I'd personally want a good, bright flash that I could see without optical aid on the dark side of a thin crescent Moon. I'm aiming for mag +1.0.

Solar output is around 1380 watts/m2, and therefore mag +1.0 is equivalent to 1.15*10^-8 watts/m2.

My eye is about 3.85*10^8m away from the Moon, meaning the flash (if hemispherically propagated) must release about 10.7GW at source. Thinking of flash-powder explosions I've seen in old films, and with reference to sites like this, once persistance-of-vision effects are factored in, I'd suggest the explosion would need to take a tenth of a second or so. Therefore I'd need 1.07 GJ of powdered magnesium and potassium perchlorate: given that it's basically an explosive, that's around about a quarter-tonne...

Andy (not obviously related to Robert) Goddard

[Bob Shaw]

Let's see - back of an enveloping:

The Sun shines at mag -26.7. I'd personally want a good, bright flash that I could see without optical aid on the dark side of a thin crescent Moon. I'm aiming for mag +1.0.

Solar output is around 1380 watts/m2, and therefore mag +1.0 is equivalent to 1.15*10^-8 watts/m2.

My eye is about 3.85*10^8m away from the Moon, meaning the flash (if hemispherically propagated) must release about 10.7GW at source. Thinking of flash-powder explosions I've seen in old films, and with reference to sites like this, once persistance-of-vision effects are factored in, I'd suggest the explosion would need to take a tenth of a second or so. Therefore I'd need 1.07 GJ of powdered magnesium and potassium perchlorate: given that it's basically an explosive, that's around about a quarter-tonne...

Andy (not obviously related to Robert) Goddard

I think I'd rather not have been the range safety officer, or had to fuel the rocket!

I wonder if they'd have launched with an expected impact on July the fourth?

Bob Shaw

[ljk4-1]

I think I'd rather not have been the range safety officer, or had to fuel the rocket!

I wonder if they'd have launched with an expected impact on July the fourth?

Bob Shaw

I think Goddard expected to the flash to be seen with less powder. I recall reading one of his contemporaries criticising this aspect of his concept, not so much the idea of a rocket reaching the Moon.

[AndyG]

I think Goddard expected to the flash to be seen with less powder.  I recall reading one of his contemporaries criticising this aspect of his concept, not so much the idea of a rocket reaching the Moon.

Goddard might be right: I estimated a mag 1.0 flash would be visible with around 250kg of powder. But the joy of magnitudes, of course, is that they're logarithmic: a just-visible, edge-of-the-naked-eye-envelope magnitude 6.0 flash would require a hundred times less powder - i.e. 2.5kg. Conversely, that should produce a flash that would be easily visible in binoculars.

Intriguingly, the descent engine of the LEM produced a not dissimilar amount of power to the ignition of this smaller quantity of powder. Given that much of that energy was released in the form of heat, I wonder if - once the CEV is flying - a smallish aperture, IR-equipped, amateur telescope could be used to track future manned vehicles at the Moon?

Andy

[Bob Shaw]

I wonder if - once the CEV is flying - a smallish aperture, IR-equipped, amateur telescope could be used to track future manned vehicles at the Moon?

Andy

Andy:

Seems reasonable, especially if the burn takes place when the vehicle is against a cold, dark background, such as space or the pre-dawn surface. Maybe even optical...

Bob Shaw