Old Blogdrive Posts 5

Tuesday, July 27, 2004
Discovery arrives at Titan…

Back to our major theme – the fictional Discovery mission to Saturn and Titan. Once Discovery crosses into Saturn’s Hill Sphere it has some important tasks:
# deccelerate from hyperbolic velocity
# change into Titan’s orbital plane
# line up an intercept orbit for Titan
# deccelerate into orbit around Titan
# land on Titan

Cassini – and Baxter’s Discovery presumably – deccelerated into a highly elliptical orbit, then maneuvered into a Titan approach orbit. Cassini’s current orbital path – modified from the originally planned Titan approach to improve communication with Huygens – needs two major maneuvers:
# Saturn Orbital Insertion (SOI) – about 626 m/s
# Periapsis raise – about 391 m/s

The SOI was completed successfully, though Cassini plowed through substantial amounts of dust nothing fatally injured the vehicle. The periapsis raising maneuver should go smoothly as well being a shorter main engine burn than the SOI.

The fictional Discovery suffered a decompression from a ring-plane impact, but otherwise successfully arrived. Baxter’s described decceleration level was actually about 10 times too high – 1/10th of a gee instead of the actual 1/100th. The Shuttle’s OMS is actually only capable of about ~ 2/100th gee. Poetic license I guess.

A direct braking into a Titan approach orbit would take a dv of ~ 1,400 m/s, but Titan is unlikely to be so obligingly in the right part of its orbit to be approached so directly. And I can’t currently work out where Titan really would be with respect to a real Discovery in circa 2014 AD, but I’m working on it ;-)

However a direct approach is not the best. To minimise propellant load Discovery needs to aerobrake in Titan’s upper atmosphere to shed its relative velocity and a direct orbit doesn’t minimise that relative velocity. An indirect approach from a higher orbit with Titan’s radius as the periapsis has a better chance of minimising the relative velocity.

For example
# Cassini’s current orbit would have required aerobraking at 8.32 km/s (29,950 km/h) which is higher than the Shuttle’s usual aerobraking range.
# A direct approach would require aerobraking at 5.38 km/s (19,400 km/h.)
# An apoapsis at 210 Saturn radii with Titan at the periapsis (20.273 radii) means aerobraking at a mere 3.26 km/s (11,740 km/h.)

Shedding a mere ~ 1,375 m/s for a 4 hour parking orbit means a lower heating load. Propellant needed for the two maneuvers is also lower than the direct orbit, saving about 320 m/s of delta-v. The penalty is the +30 weeks spent getting into the right orbital positions.
Posted at 3:15 pm by Adam
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Monday, July 26, 2004
Solar Power Satellites

In the late 1960s physicist Peter Glaser proposed to build huge solar energy collecting satellites, but no one took him seriously in the age of cheap oil and “safe” nuclear power. Then the Oil Crunch of the mid-70s hit and the US Department of Energy (DoE) and NASA took him seriously. The Solar Power Satellites (SPS) they designed were typically capable of delivering 10 gigawatts power to the ground, with about 62.9% efficiency. In space that meant 129 km^2 arrays of solar cells massing perhaps ~ 80 – 100 thousand tons, beaming power to the ground as microwaves.

Their designs made a lot of assumptions that made them difficult –
# on-orbit assembly was assumed with a huge work-force and inter-orbital transportation system requiring everything haulled from the ground, cargo haulled to GEO via giant ion-drive space-tugs and faster chemical fuel tugs delivering workers
# arrays were supported by rigid frameworks that had to be assembled on-orbit
# power transmission was at lower microwave frequencies that minimised atmospheric absorption, but need huge transmitting antennae
# the solar array had to track the Sun continuously and the antenna had to point to the power receiver continuously
# huge dedicated cargo delivery aerospace vehicles had to be developed for the program to deliver equipment to LEO

Each assumption complicates design and increases cost and mass delivered to the target orbit. Geoffrey Landis, a physicist who works for NASA and writes SF, has discussed SPS alternatives extensively. He has several interesting papers at his web-page…

Landis technical papers online

…scroll down and you will find the SPS section. The first article in the list is the most recent and well worth a read. He proposes a serious rethink of all assumptions about SPS and then describes a system that is nearly viable for power supply today.

His next article on Super-Synchronous SPS provides a good description of an ultra-light weight system. Compare it to the old DoE/NASA SPS satellites – its inflatable, uses advanced concentrators, doesn’t need a separate, rotating transmitter, can supply power from the beginning and only masses 1,300 tons for 1 to 2 gigawatts power supplied to the ground.

An alternative for transporting SPS is to deploy an array sub-unit at LEO and use its power for an ion/plasma drive to move it to GEO and/or L1/2. Potentially this approach will cut mass delivered to LEO to a mere 30% of trying to do it all via chemical rockets. The apparently defunct PowerSat corporation tried to patent this concept, but I believe that this article…

Electric Propulsion for SSPS

…indicates a prior useage.
Posted at 12:58 pm by Adam
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Buran to Saturn

Buran

In some ways the Russian Space Shuttle Buran is a superior vehicle to the USA’s Shuttle. More payload, more fuel, better Isp, less dead weight. And no clunky Main Engines on the Orbiter – which doesn’t use them in space. However that’s the liability as well – can’t launch it except via an Energia, and there aren’t too many of them around. Fewer than the Saturn Vs.

But despite the sole Energia still sitting in its hangar while its boosters are being used by Sealaunch as Zenit launchers, Buran is a nice machine. Its OMS equivalent uses LOX/Kerosine with an Isp ~ 362 seconds. Now I’m not sure what the long term storage capability of LOX is – it is cryogenic, but it’s not a “hard” cryogen like hydrogen. I don’t think it has the boil-off issues that hydrogen does and certainly actively cooling it won’t take as much power or equipment as LH2. For the deep space maneuvers needed to cruise to Saturn Cassini-style and to reach Titan safely, about 1,650 m/s dv is needed. An exhaust velocity of 3,550 m/s is better than the Shuttle’s 3,072 m/s, needing less fuel and tankage.

Buran’s payload bay is also a bit bigger, but I think its power system is a bit behind the Shuttle’s. All in all it would be potentially a better vehicle to send to Saturn than the NASA Shuttle Orbiter.

Encyclopedia Astronautica on Buran
Posted at 12:37 pm by Adam
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Sunday, July 25, 2004
Quantum Breakthrough…

New Scientist has just published a possible experimental falsification of several interpretations of Quantum Mechanics, notably the Copenhagen and Many Worlds Interpretations. What remains viable is John Cramer’s Transactional Interpretation – that the quantum wave-function travels forward and backward in time in any interaction, creating a “handshake” to exchange energy/momentum/spin etc. Cramer’s daughter, Kathryn, has placed a number of links and discussions of the new claim online here… Kathryn on Quantum

…the Physics community has been abuzz about this one since at least April. Would be nice to see more replications of Shahriar’s experiment.

John’s site is here… John Cramer

…he discusses his Interpretation here… Transactional Interpretation Explained

…and here…

Explained Clearly [this is the more accessible explanation]

…if this pans out then it will have interesting consequences. Many Worlds has a lot of advocates and won’t die easily. But for my money it’s a philosophical mess. Creates a new World for every quantum choice which seems rather excessive. But have a read of this one… Many Worlds in one …in an infinite Universe all physical histories are physically real – somewhere Out There. John Cramer has written extensively on wormholes at a popular level. Here’s an interesting discussion from a few years ago… Wormhole Conference

Enjoy!
Posted at 12:32 am by Adam
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Spin Gravity Adaptable…

A common criticism of 2001: A Space Odyssey is the size of the 1/6th gee centrifuge – “it’s too small”. At 35′ across (radius = 5.334 m, g = 1.622 m/s^2) the centrifuge is spinning at ~ 5 rpm. Common objection is that Dave and Frank will be unable to adjust to the Coriolis forces, chucking up their SpaceFood packs for the whole trip. However Greg Benford and George Zebrowski in their anthology Sky Life note that 6 rpm is fine and up to 10 rpm is adaptable, based on the only real biomedical work done in the ’60s. Well now it seems that the old data was right – NASA’s latest news update… Spin Gravity News

… test subjects could adjust to spin rates as high as 25 rpm. For seated tasks, mind you, but there is no in principle objection to walking around at lower spin-rates. At 6 rpm a one-gee centrifuge has a 25 metre radius, and a Mars-gee (~ 0.378 gee) just 10 metres. At 10 rpm the respective radii are ~ 9 metres and 3.4 metres. Providing substantial spin gravity should be feasible for relatively small vehicles and habitats – thus the “zero-gee is bad for us” objection to in-space living is missing the point: no one needs to live in zero-gee all the time.

Another point is that it makes inflatable habitats more attractive – toroids (“inner tubes”) were extensively studied in the early 1960s. Easy to inflate and rotate. Shield it within a plasma sheath and the habitat will be safe from solar storms and the Jovian magnetosphere. And you can use the plasma shield as a plasma sail to gradually spiral out to any of the outer planets and their extensive moon systems.
Posted at 12:26 am by Adam
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Friday, July 23, 2004
Discovery – a first estimate

More on flying to Titan in a Shuttle.

Firstly, how much does Discovery weigh?

Discovery

77,564 kg empty, with main engines (at launch.)

68,682 kg empty, without (after launch.)

A Shuttle can carry 10,830 kg of OMS propellant, plus 3,273 kg RCS propellant – 14,103 kg total. Both systems use N2O4/MMH which is indefinitely storable in space, just like Cassini’s rocket system.

The fictional Discovery’s payload consists of :

# ISS Habitation module (~ 10,000 kg)

# Spacelab pressurised module as CELSS farm (~ 7,000 kg)

# docking node (~1,800 kg)

# 2 slightly modified Apollo Command Modules (5,900 kg each)

# several Russian Topaz nuclear reactors (~ 1,000 kg each)

All up, considering how vague Baxter was, that’s about ~ 33,400 kg extra. The CELSS farm is supposed to recycle the crew’s supplies, their waste dissociated by a Super Critical Water Reactor – extremely hot steam at high pressure which breaks up virtually all organics into basics. Oxygen can be cracked from carbon dioxide via electricity, the CO2 itself adsorbed by zeolite beds in the air system.

If we throw in supplies for five for ~ 600 days @ 1.27 kg/day.pp that’s another 3,810 kg. Plus other odds and ends make it ~ 50,000 kg for life-support/Titan Base. Hence Discovery is about 133,000 kg, and about ~ 130,000 kg less the tailplane.

Fuel wise Discovery needs about 1,600 m/s of maneuvering to emulate Cassini’s gravitational ballet to get to Saturn and deccelerate into a Titan approach. Using the OMS for maneuvers gives an Isp ~ 313.2 seconds (a kilo of propellant creates a kilo of thrust – 9.8 newtons – for 313.2 seconds) which means a 130,000 kg vehicle needs ~ 88,700 kg of propellant plus the propellant needed to shift the fuel tanks as well. Including the tankage (~0.11 fuel mass) it’s about 106,700 kg total – less tankage saved by fuel kept in the OMS pods, means ~ 105,000 kg total. Baxter was about right with his vague two hundred thousand pounds which means we’re on the right track.
Posted at 12:58 pm by Adam
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Thursday, July 22, 2004
Black Hole Reversal

Recently Stephen Hawking has claimed a solution to the Black Hole information paradox – simply put: What happens to a particle’s quantum information after it gets dragged into a Black Hole’s singularity? Is it mashed into oblivion by infinite curvature? Or do quantum effects mean the heart of a Black Hole isn’t a real singularity?

But just what is a singularity and why is there one in a Black Hole?

We all know Black Holes are objects with gravity so strong that light can’t escape them, but what is not often realised just what that means in our Universe. The speed of light is the speed at which space-time happens in Universe – an object with gravity strong enough to trap light will stop space-time.

So what happens then?

Space and time swap over – and everything plunges into the very centre of the Black Hole irreversibly, just like we irreversibly plunge forwards into the Future. And that very centre is the singularity, a point where mass, space and time reach infinite density.

Or so we once thought.

The problem with infinity is that it can’t be handled very well mathematically. Throw quantum particles into an infinite point and their unique quantum information gets erased by the maths – i.e. can no longer be described. So what is the solution? Is the quantum destroyed by the singularity or is the singularity ‘blurred’ into finitude by the Quantum?

That seems to be Hawking’s latest brain-wave – though he is not the first to advocate such a view – and he maybe right. But first the experts need to understand what he is really trying to say.

Hawking’s new ideas
Posted at 10:16 pm by Adam
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Beyond the Solar System

Ever wondered where the old Pioneers and Voyagers are now? The NASA ephemeris lets you plot even that. As I write it’s 19:00 local time (09:00 Universal Time)

Voyager II

2004-Jul-22 09:00

RA 295.42830 degrees, DEC -51.67501 degrees

To the Sun: 73.9165414845 AU

To the Earth: 73.0520999427 AU

Velocity relative to Sun: 15.64895 km/s

Velocity relative to Earth: 34.25218 km/s

Years/Light-year: 19,157 years

Voyager I

2004-Jul-22 09:00

RA 255.21700 degrees, DEC 12.40173 degrees

To the Sun: 92.5734838240 AU

To the Earth: 92.0072159163 AU

Velocity relative to Sun: 17.18309 km/s

Velocity relative to Earth: 40.86734 km/s

Years/Light-year: 17,447 years

Pioneer 10

2004-Jul-22 09:00

RA 76.92441 degrees, DEC 25.90554 degrees

To the Sun: 85.9551258556 AU

To the Earth: 86.7113292237 AU

Velocity relative to Sun: 12.18188 km/s

Velocity relative to Earth: 24.48707 km/s

Years/Light-year: 24,609 years

Pioneer 11

RA 278.46355 degrees, DEC -8.28760 degrees

To the Sun: 65.4895044164 AU

To the Earth: 64.5723907582 AU

Velocity relative to Sun: 11.68028 km/s

Velocity relative to Earth: 33.13585 km/s

Years/Light-year: 25,666 years

These plucky little interstellar voyagers are our first emissaries to the Stars – and I hope they are not the last. There is a company planning to send a solar-sail into interstellar space with messages and genetic samples – Team Encounter…

Solar Sails
Team Encounter’s web-site is ‘unavailable’ which hopefully doesn’t mean they’ve gone bust. L’Garde, their sail maker, are makers of advanced inflatable space structures. Cool stuff and potentially framework for ultra-light Solar Power Satellites….
Posted at 10:01 pm by Adam
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Cassini Trek update…

There’s nothing new under the Sun… or so everyone thinks when they discover their efforts are redundant. I was trying to reconstruct Cassini’s long cruise out to Saturn, and discovered that this site would do it for me for minimal effort…

Solar System Dynamics ephemeris

…this is NASA’s own Solar System Dynamics ephemeris generator and it can plot just about anything orbitting the Sun and planets down to the minute and micro-AU. By fiddling a bit with it I have generated detailed plots of Cassini’s trek. Trick is now I have to figure out relative positions and velocities for Cassini and the planets involved. That is NOT calculated so easily. Will have to work on my spherical geometry and spread-sheeting…
Posted at 5:48 pm by Adam
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Wednesday, July 14, 2004
Where are the planets Now…

Here’s a helpful web-site for tracking the planets… Planet Plot

…if you register at the main-page [it’s free] then the ephemeris calculator will work things out for your location too. But just getting the daily low down on the planets is cool.

Very helpful for reconstructing Cassini’s trek, for example.
Posted at 9:20 am by Adam
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