Randall Clague | 1 Jul 09:13 2002
Picon

Re: A Rocket A Day

On Sat, 22 Jun 2002 02:41:48 +0100, Ian Woollard
<i.woollard <at> btinternet.com> wrote:

>http://www.ghg.net/redflame/launch.htm

New to me was Whitehead pointing out that although space nuts use SSTO
and RLV interchangeably, the two are almost mutually exclusive: SSTO
has to be light, and RLV has to be rugged.  Doing an SSTO RLV...
We're going to sneak up on it from both directions, improving the
performance of our RLV until a stripped down version will just make
orbit with no payload - and then we'll try to improve it some more.

>It's got some very interesting bits, particularly when he talks about 
>the safety of LOX...
>not sure I agree with his conclusions overall. I would be interested on 
>this groups opinion on how
>the behaviour of LOX compares with HTP though.

That's a religious question here.  "There is no oxidizer but peroxide,
and silver is its prophet."  Because it can be used as a monoprop,
peroxide is the best propellant to use when you're learning how to do
liquid fuel rocketry.  It's simple and it's safe.

The downside is its cost.  Paying several dollars per pound for
peroxide is not an unusual experience.  LOX costs about 1% of that, so
any large biprop operation cries out economically for LOX.  Peroxide
need not cost as much as it does, and we're working on ways of
reducing its cost, but if we ever get HTP cost down to LOX cost it'll
be a miracle.

(Continue reading)

Randall Clague | 1 Jul 09:13 2002
Picon

Drag losses vs. gravity losses (was: New lube, VTVL in Israel and TRIZ)

On Sat, 15 Jun 2002 12:40:28 -0700, Randall Clague
<rclague <at> rclague.net> wrote:

>As you've discovered, SSTO with a small vehicle requires trajectory 
>optimization, which in turn is a balancing act as you trade off drag losses 
>against gravity losses.  There is probably a minimum size (for a given 
>shape, mass fraction, propellant type, engine, etc.) below which a single 
>stage vehicle can't make orbit.

So I did a structural model for this really cool pressure fed TSTO.
Nothing fancy, 6061 T6, about 1000 kg GLOW, 10 kg payload, delta-v
9000 m/sec.  You could take the thing out to the launch site in a
small U-Haul truck, and put 22 lbs in orbit for about $1000/lb.
Definitely within the reach of motivated amateurs, and probably
marketable as well.  Way cool.

Next step, trajectory modeling.

Drag *killed* me.  It didn't even make a decent sounding rocket.

I'm currently doing a parametric analysis, varying thrust, propellant
load, aspect ratio, and payload.  What I've seen just from the first
few runs is that crawling along through the troposphere at M 0.5 or so
gets me the best final altitude.  I throw away a lot of fuel "standing
on a pillar of fire," as Mitch puts it, but the alternative is burning
harder to get through the atmosphere quicker.  This decreases my
gravity losses at the price of increasing my drag losses even more.
(Gravity losses are linear, but drag is proportional to the square of
the velocity.)

(Continue reading)

GDNordley | 1 Jul 15:48 2002
Picon

Re: Drag losses...

Gentlefolk,

<<... delta-v 9000 m/sec.... >>

The canonical figure  is 10 km/s, despite a paper about ten years ago that 
fooled me and some others.  Schemes to make any significant dent in that have 
born little fruit.  If you accelerate faster to avoid gravity losses, your 
engines are heavier and you have more drag in the lower atmosphere.  Wings 
let you use smaller engines, but cost mass and drag.  High pressure pump fed 
engines are lighter and more efficient, but pumps eat mass budget.   
Trajectory optimization buys you a tenth of a km/s or something.  I won't 
quarrel with a tenth of a km/s here or there and all that stuff is in the 
direction of goodness, but I suggest one take a deep breath, design for 10 
km/s, and treat anything better than that as margin.

--Best, Gerald
cpwinter | 1 Jul 18:38 2002
Picon
Picon

OT: George Dyson's latest book: Project Orion

This is a cracking good read.  I bought it on Saturday and finished it 
Sunday.

But I was surprised to find it made me less sanguine about Orion than I 
had been.  There are, apparently, some fundamental unsolved problems 
with the concept.  When I say "fundamental", I mean it in the engineering 
sense, not in the sense of something contravening physical laws.

For one thing, there is the question of excessive pusher-plate ablation -- 
which would have been settled if that one underground test had been 
approved.

Then there are those shock absorbers!

But fallout remains the most vexing problem. I did not know that any 
produced within Earth's magnetosphere eventually makes it to the 
planet's surface.

The book is well-written, thoroughly researched, and makes few 
mistakes.  I recommend it highly.

Chris
Michael Wallis | 1 Jul 19:00 2002

Next Meeting ...

The next meeting of the Experimental Rocket Propulsion Society will be
held this THURSDAY evening at the IHOP starting at 8:00pm.

Items for meeting #240 (04 Jul 2002):

 - Admin Teams
        - CMT
        - Documentation
        - IT
        - Liaisons
        - Logistics
        - PAO
        - Treasurer
    - Development Teams
        - Chief Scientist
        - Flight Controls
        - Propellants
        - Regulatory Issues
        - Safety
        - Testing
    - Project Status
        - GizmoCopter
        - SmartFlight
        - KISS
        - Spike
        - POGO

The address is:

        International House Of Pancakes
(Continue reading)

Bill Clawson | 1 Jul 19:20 2002

RE: Next Meeting ...

We're having a meeting on the 4th of July??  I won't be able to attend due
to familial obligations.

Bill

 -----Original Message-----
From: 	Michael Wallis [mailto:mwallis <at> Ceres.wallis.com] 
Sent:	Monday, July 01, 2002 10:00 AM
To:	erps-list <at> lists.erps.org
Subject:	[ERPS] Next Meeting ...

The next meeting of the Experimental Rocket Propulsion Society will be
held this THURSDAY evening at the IHOP starting at 8:00pm.

Items for meeting #240 (04 Jul 2002):

 - Admin Teams
        - CMT
        - Documentation
        - IT
        - Liaisons
        - Logistics
        - PAO
        - Treasurer
    - Development Teams
        - Chief Scientist
        - Flight Controls
        - Propellants
        - Regulatory Issues
        - Safety
(Continue reading)

David Masten | 1 Jul 19:32 2002

RE: Next Meeting ...

Something just not right about a meeting on a holiday.

No official meeting on July 4.

If y'all want to meet and shoot the breeze anyway, I'm up for it.

Dave
Randall Clague | 1 Jul 20:23 2002
Picon

Re: Re: Drag losses...

On Mon, 1 Jul 2002 09:48:45 EDT, GDNordley <at> aol.com wrote:

>The canonical figure  is 10 km/s, despite a paper about ten years ago that 
>fooled me and some others.  Schemes to make any significant dent in that have 
>born little fruit.  If you accelerate faster to avoid gravity losses, your 
>engines are heavier

That's actually what started all this.  "Gee, do I really need those
big heavy high thrust engines...?"  Yes.

-R

--
"Sutton is the beginning of wisdom -
but only the beginning."
                     -- Jeff Greason
David Masten | 1 Jul 20:31 2002

Re: Re: Drag losses...

On Mon, 2002-07-01 at 11:23, Randall Clague wrote:

> That's actually what started all this.  "Gee, do I really need those
> big heavy high thrust engines...?"  Yes.
> 

Randall,

What Cd did you use? Drag should be around 5% of dV.

Dave
Randall Clague | 1 Jul 20:37 2002
Picon

Re: Re: Drag losses...

On 01 Jul 2002 11:31:02 -0700, David Masten <dmasten <at> piratelabs.org>
wrote:

>What Cd did you use? 

0.7.  I use only numbers I'm sure we can make, and we've already
demonstrated CD = 0.7.

>Drag should be around 5% of dV.

Depends on the size of the vehicle.  Remember square/cube law becomes
significant at small scales, especially with that squat shape on which
Michael insists.  I'm beginning to think squat *and* small won't work.

-R

--
"Sutton is the beginning of wisdom -
but only the beginning."
                     -- Jeff Greason

Gmane