Date: Wed, 05 Jul 2000 22:25:33 -0700
From: Doug Jones <random@qnet.com>
Newsgroups: sci.space.policy
Subject: Re: Ballooning on Mars

Serial # 19781010 wrote:
>
> Ballooning on Mars
>
> Balloons present excellent opportunities for exploring Mars.
> Unfortunately, the logistical problems are severe.  I am interested in
> hearing from anyone who has insight into the following:
>
> Martian atmosphere is 0.9 per cent as dense as Earth.  To generate
> lift, a balloon would have to displace huge volumes of atmosphere.  I
> have calculated that to lift 10kg of payload on Mars, a balloon would
> need to be approximately 25m in diameter.  This assumes material
> weight of 55g/sq metre, totalling 108kg.  It would require about 6.5kg

Yow!  That's a *thick* balloon!  Assuming almost any plastic at density
of about 800 kg/m3, that's 2.7 mils, about ten times the typical
thickness of high altitude balloons.

In 1997 I launched a Raven Industries N25-2.5L-0.300 zero pressure
balloon.  From the spec sheet:

Type: Natural shape, tapeless (no reinforcing tapes attached to the
film)
Volume: 300,000 ft3
Weight: 31.3 lbs
Inflated height x diameter: 76x90 ft
Nominal Load: 25 lbs
Nominal Altitude: 134,300 ft (10 lb payload to 145K ft, no guarantees)
Film gauge: 0.25 mil (dry-cleaner's bag thin)
Surface area: 22,860 ft2  (!)
Length: 129 ft (before inflation)

Plug the .25 mil (6 micron) thickness into your spreadsheet and you'll
get much better results.

--
Doug Jones
Rocket Plumber, XCOR Aerospace
http://www.xcor-aerospace.com

Newsgroups: sci.space.tech
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Stupid enough to work?
Date: Sat, 26 Aug 2000 20:26:43 GMT

In article <39A494E3.BDDF4B62@cableregina.com>,
kevin smith  <kevsm1@cableregina.com> wrote:
>...A balloon large enough to loft a
>manned vehicle plus booster would be BIG...

For purposes of reference, a handy round number is that you need (very
roughly) a cubic meter of hydrogen or helium to lift a kilogram.
--
Microsoft shouldn't be broken up.       |  Henry Spencer   henry@spsystems.net
It should be shut down.  -- Phil Agre   |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.tech
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Stupid enough to work?
Date: Mon, 28 Aug 2000 03:51:08 GMT

In article <0V7q5.22942$Xg.579141@news-east.usenetserver.com>,
Ian Stirling  <Inquisitor@I.am> wrote:
>>For purposes of reference, a handy round number is that you need (very
>>roughly) a cubic meter of hydrogen or helium to lift a kilogram.
>
>That's at sea level though.
>For every 6Km (or so) you go up, the amount needed doubles.

The *volume* needed doubles... but the gas helpfully looks after this
automatically, because that 1m^3 becomes 2m^3 as the pressure drops.
Until the atmospheric composition actually starts to change, at truly
extreme altitude, the lift provided by a given mass of gas is constant.
It effectively has a negative weight, which does not change as it expands
and contracts with changes in temperature and pressure, provided those
changes match those in the surrounding atmosphere.

Mind you, there is one caveat to this:  the balloon has to be able to
contain those volume changes.  That's where the tradeoffs come in, because
a balloon which can accommodate (say) a 5:1 expansion will be larger and
heavier than one which can only handle a 2:1 expansion.
--
Microsoft shouldn't be broken up.       |  Henry Spencer   henry@spsystems.net
It should be shut down.  -- Phil Agre   |      (aka henry@zoo.toronto.edu)