$5M Moon Rock Stolen From Malta Museum

"Scott Hedrick" wrote in message ...
"Henry Spencer" wrote in message
...
There was even an early-70s proposal to commercially finance a final
Apollo mission, although it didn't get very far, at least partly because
NASA's reaction was total hostility.

Which it would still be, but they'd do it, because now they wouldn't get
funds any other way.

Why aren't we selling advertising on our birds?


Who would see it? On the other hand, if you were to provide
something people do want to see, like their neighborhood, city and
faraway places from a new perspective, down to a resolution of 15ft or
so, you might have space to sell.
Several 10cm (4in) telescopes attatched to a boom on the ISS might
be worth more than three times their weight in gold, which is what it
would cost to build, launch and install. Two or three motorized pan
telecameras, for the cost of a one minute spot during the super bowl.
It would be a boon for NASA as well, which should make the
administration amenable to the idea.
It gives the notion of "space available" a whole earth of new
meaning.

Stephen Kearney

"Jim Davis" wrote in message
. 1.4...
johnhare wrote:

Too close to perfection. The ALS (Advanced Launch System)
program
that cost $1B and ended in 1989, determined that dropping the
chamber pressure from 3000 to 2250psi, and the horspower of
the turbo pumps from 100hp per pound to 37, would result in a
specific impulse drop of 460 seconds to 420.

This doesn't sound right. The RL10 gets better vacuum Isp than
that with far less pressure.

But the RL-10 rarely has to work at sea level so it can have the high
expansion ratios to give high vacuum Isp at low chamber pressures.
The RL-10s for the DC-X which did operate at sea level had severely
truncated nozzles which would have hurt vacuum Isp badly.

The 460 seconds clearly was a vacuum Isp he was refering to. If it had
been 360 vs 320 seconds, then it would have been sea level performance.
Starting at sea level, you do need the high pressures to get performance,
which is your point. Out of context, I'm not sure what performance hit
was being refered to if not just the vacuum Isp.

Jim Davis

"johnhare" wrote in message
om...

This doesn't sound right. The RL10 gets better vacuum Isp than
that with far less pressure. You are aware I was joking? Just to
make it clear, current rocket engines are barely started in terms
of what they need to be. Anything you consider to be perfect is
something you have decided you can't improve. Perfection is an
illusion of a limited mind.


There does come a point of diminishing returns, where it is not
particularly worth improving. If one considers the ideal minimalistic
chemical rocket engine to just be a pressure vessel, then one can only
approach this fundamental limit. Having said that, I think a T/W of a
1000 is not inconceivable, at substantially lower cost and marginally
better ISP.

Pete.

"Old Physics" wrote in message
om...
"Scott Hedrick" wrote in message
...
"Henry Spencer" wrote in message
...
There was even an early-70s proposal to commercially finance a final
Apollo mission, although it didn't get very far, at least partly
because
NASA's reaction was total hostility.

Which it would still be, but they'd do it, because now they wouldn't get
funds any other way.

Why aren't we selling advertising on our birds?


Who would see it?

I would. I watch launches. Don't you?

On the other hand, if you were to provide
something people do want to see, like their neighborhood, city and
faraway places from a new perspective, down to a resolution of 15ft or
so, you might have space to sell.

Terraserver.

It would be a boon for NASA as well,

Let's see the math.

johnhare wrote:

The 460 seconds clearly was a vacuum Isp he was refering to. If it had
been 360 vs 320 seconds, then it would have been sea level performance.
Starting at sea level, you do need the high pressures to get performance,
which is your point. Out of context, I'm not sure what performance hit
was being refered to if not just the vacuum Isp.

Was the engine also intended to operate at sea level? In that case,
dropping the chamber pressure would also force the expansion ratio to
be reduced, which would affect vacuum Isp.

Paul
who wonder why they aren't using any of those
nozzle tricks that would get around this

On Mon, 31 May 2004 23:03:58 -0700, Old Physics wrote:

"Scott Hedrick" wrote in message
...
"Henry Spencer" wrote in message
...

snip

Why aren't we selling advertising on our birds?


Who would see it? On the other hand, if you were to provide
something people do want to see, like their neighborhood, city and
faraway places from a new perspective, down to a resolution of 15ft or
so, you might have space to sell.

Companies already sell fraction of a meter resolution photography for
relatively affordable prices. I even heard of an alleged advertising
gimmick for a magazine that supposed would show a satellite picture of
your mailing address on the front cover of the first issue they sent you.
Maybe it's an urban myth?

Also, there would be ways to make sure advertising is seen even if they
had to fly a camera up with the bird.


Karl Hallowell

johnhare wrote:

The 460 seconds clearly was a vacuum Isp he was refering to. If
it had been 360 vs 320 seconds, then it would have been sea
level performance. Starting at sea level, you do need the high
pressures to get performance, which is your point. Out of
context, I'm not sure what performance hit was being refered to
if not just the vacuum Isp.

The point is, John, that you are unfairly comparing an engine that is
designed almost exclusively for vacuum (the RL-10) to one that has to
operate at sea level also (the ALS/NLS engine). If an engine has to
operate at sea level, chamber pressures have to be high to avoid
gross overexpansion and flow separation with the expansion ratios
necessary to acheive high Isp in vacuum. If the engine is going to
operate only in vacuum overexpansion is not a concern so low chamber
pressures are not inconsistent with high Isp.

In other words, when the chamber pressure of the ALS/NLS engine was
lowered, the expansion ratio had to be lowered as well to avoid gross
overexpansion at sea level. The reduction in expansion ratio hurt
vacuum Isp.

Jim Davis

"Jim Davis" wrote in message
. 1.4...
johnhare wrote:

The 460 seconds clearly was a vacuum Isp he was refering to. If
it had been 360 vs 320 seconds, then it would have been sea
level performance. Starting at sea level, you do need the high
pressures to get performance, which is your point. Out of
context, I'm not sure what performance hit was being refered to
if not just the vacuum Isp.

The point is, John, that you are unfairly comparing an engine that is
designed almost exclusively for vacuum (the RL-10) to one that has to
operate at sea level also (the ALS/NLS engine). If an engine has to
operate at sea level, chamber pressures have to be high to avoid
gross overexpansion and flow separation with the expansion ratios
necessary to acheive high Isp in vacuum. If the engine is going to
operate only in vacuum overexpansion is not a concern so low chamber
pressures are not inconsistent with high Isp.

I had assumed that any serious advanced engine concept would not
take a 40 second Isp hit purely on lack of adequate expansion ratio.
Obviously I didn't run any numbers first, and didn't take the time to
look it up. So if I was being unfair, apologies to any affected parties.

In other words, when the chamber pressure of the ALS/NLS engine was
lowered, the expansion ratio had to be lowered as well to avoid gross
overexpansion at sea level. The reduction in expansion ratio hurt
vacuum Isp.

I will have to do some checking.
I will not post before my morning coffee.
I will not post before my morning coffee.
I will not post before my morning coffee.

Jim Davis

On or about Tue, 1 Jun 2004 08:12:08 -0400, Scott Hedrick made the sensational claim that:
I watch launches. Don't you?

Yes, but I don't really have a choice sometimes. And I *always* listen to them
at least. :-)
--
This is a siggy | To E-mail, do note | Just because something
It's properly formatted | who you mean to reply-to | is possible, doesn't
No person, none, care | and it will reach me | mean it can happen

"Karl Hallowell" wrote in message
news
Companies already sell fraction of a meter resolution photography for
relatively affordable prices.

Companies also already buy advertising on rockets. Google and you should
easily find a picture of the Pizza Hut Russian rocket.