aerobraking

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Despite its drawbacks, the Dual-Keel design offered many possibilities for servicing exploration missions.  Depicted here are a variety of possible upgrades, involving spacecraft construction servicing and transfer.  

Seen here are various ideas for what this might allow.  From Lunar aerobraking ships to a possible Mars vehicle and a large bay designed to repair satellites and to stage interplanetary probes for launch.  

It should be noted that before the project became the ISS, it orbited at a very different inclination, one more favorable to exploration mission departures.

This front “shield” is what makes Kronos 1 an unique spacecraft. It is designed to act as radiation shield and aerobraking heatshield for braking at all three major Kronos 1 destinations - Mars, Jupiter and Saturn.

In his talk today, Musk presented a number of interesting and very useful ideas. I don’t think they are practical in the form he presented them. But with a little modification, they could be made practical and very powerful. He’s right on the mark about using methane/oxygen propellant, which can be made on Mars; about making the spacecraft reusable, and refillable on orbit.
The key thing I would change is his plan to send the whole trans Mars propulsion system all the way to Mars and back. Doing that means it can only be used once every four years. Instead he should stage off of it just short of Earth escape. Then it would loop around back to aerobrake into Earth orbit in a week, while the payload habitat craft with just a very small propulsion system for landing would fly on to Mars.
Used this way, the big Earth escape propulsion system could be used 5 times every launch window, instead of once every other launch window, effectively increasing its delivery capacity by a factor of 10. Alternatively, it could deliver the same payload with a system one tenth the size, which is what I would do.
So instead of needing a 500 ton launch capability, he could send the same number of people to Mars every opportunity with a 50 ton launcher, which is what Falcon heavy will be able to do.
The small landing propulsion unit could either be refilled and flown back to LEO, used on Mars for long distance travel, or scrapped and turned into useful parts on Mars using a 3D printer.
Done in this manner, such a transportation system could be implemented much sooner, possibly before the next decade is out, making settlement of Mars a real possibility for our time.
Venus Express goes gently into the night
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ESA Venus Express Mission patch.

16 December 2014

ESA’s Venus Express has ended its eight-year mission after far exceeding its planned life. The spacecraft exhausted its propellant during a series of thruster burns to raise its orbit following the low-altitude aerobraking earlier this year.

Since its arrival at Venus in 2006, Venus Express had been on an elliptical 24‑hour orbit, traveling 66 000 km above the south pole at its furthest point and to within 200 km over the north pole on its closest approach, conducting a detailed study of the planet and its atmosphere.

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Visualisation of the Venus Express aerobraking manoeuvre
However, after eight years in orbit and with propellant for its propulsion system running low, Venus Express was tasked in mid-2014 with a daring aerobraking campaign, during which it dipped progressively lower into the atmosphere on its closest approaches to the planet.

Normally, the spacecraft would perform routine thruster burns to ensure that it did not come too close to Venus and risk being lost in the atmosphere. But this unique adventure was aimed at achieving the opposite, namely reducing the altitude and allowing an exploration of previously uncharted regions of the atmosphere.

The campaign also provided important experience for future missions – aerobraking can be used to enter orbit around planets with atmospheres without having to carry quite so much propellant.

Between May and June 2014, the lowest point of the orbit was gradually reduced to about 130–135 km, with the core part of the aerobraking campaign lasting from 18 June to 11 July.

After this month of ‘surfing’ in and out of the atmosphere at low altitudes, the lowest point of the orbit was raised again through a series of 15 small thruster burns, such that by 26 July it was back up to about 460 km, yielding an orbital period of just over 22 hours.

The mission then continued in a reduced science phase, as the closest approach of the spacecraft to Venus steadily decreased again naturally under gravity.

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Venus Express aerobraking
Under the assumption that there was some propellant still remaining, a decision was taken to correct this natural decay with a new series of raising manoeuvres during 23–30 November, in an attempt to prolong the mission into 2015.

However, full contact with Venus Express was lost on 28 November. Since then the telemetry and telecommand links had been partially re-established, but they were very unstable and only limited information could be retrieved.

“The available information provides evidence of the spacecraft losing attitude control most likely due to thrust problems during the raising manoeuvres,” says Patrick Martin, ESA’s Venus Express mission manager.

“It seems likely, therefore, that Venus Express exhausted its remaining propellant about half way through the planned manoeuvres last month.”

Unlike cars and aircraft, spacecraft are not equipped with fuel gauges, so the time of propellant exhaustion for any satellite – especially after such a long time in space – is difficult to predict. The end could not be predicted but was not completely unexpected either.

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Venus
Without propellant, however, it is no longer possible to control the attitude and orient Venus Express towards Earth to maintain communications. It is also impossible to raise the altitude further, meaning that the spacecraft will naturally sink deeper into the atmosphere over the coming weeks.

“After over eight years in orbit around Venus, we knew that our spacecraft was running on fumes,” says Adam Williams, ESA’s acting Venus Express spacecraft operations manager.

“It was to be expected that the remaining propellant would be exhausted during this period, but we are pleased to have been pushing the boundaries right down to the last drop.”

“During its mission at Venus, the spacecraft provided a comprehensive study of the planet’s ionosphere and atmosphere, and has enabled us to draw important conclusions about its surface,” says Håkan Svedhem, ESA’s Venus Express project scientist.

Venus has a surface temperature of over 450°C, far hotter than a normal kitchen oven, and its atmosphere is an extremely dense, choking mixture of noxious gases.  

One highlight from the mission is the tantalising hint that the planet may well be still geologically active today. One study found numerous lava flows that must have been created no more than 2.5 million years ago – just yesterday on geological timescales – and possibly even much less than that.

Indeed, measurements of sulphur dioxide in the upper atmosphere have shown large variations over the course of the mission. Although peculiarities in the atmospheric circulation may produce a similar result, it is the most convincing argument to date of active volcanism.

Even though the conditions on the surface of Venus are extremely inhospitable today, a survey of the amount of hydrogen and deuterium in the atmosphere suggests that Venus once had a lot of water in the atmosphere, which is now mostly gone, and possibly even oceans of water like Earth’s.

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Is Venus volcanically active?
Also just like Earth, the planet continues losing parts of its upper atmosphere to space: Venus Express measured twice as many hydrogen atoms escaping out of the atmosphere as oxygen atoms. Because water is made of two hydrogen atoms and one oxygen atom, the observed escape indicates that water is being broken up in the atmosphere.

Studies of the planet’s ‘super-rotating’ atmosphere – it whips around the planet in only four Earth-days, much faster than the 243 days the planet takes to complete one rotation about its axis – also turned up some intriguing surprises. When studying the winds, by tracking clouds in images, average wind speeds were found to have increased from roughly 300 km/h to 400 km/h over a period of six Earth years.

At the same time, a separate study found that the rotation of the planet had slowed by 6.5 minutes since NASA’s Magellan measured it before completing its five-year mission at Venus 20 years ago. However, it remains unknown if there is a direct relationship between the increasing wind speeds and the slowing rotation.

“While the science collection phase of the mission is now complete, the data will keep the scientific community busy for many years to come,” adds Håkan.

“Venus Express has been part of our family of spacecraft in orbit since it was launched in 2005,” says Paolo Ferri, Head of ESA Mission Operations.

“It has been an exciting experience to operate this marvellous spacecraft in the Venus environment. The scientific success of the mission is a great reward for the work done by the operations teams and makes us more proud than sad in this moment of farewell.”

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Venus, southern hemisphere
“While we are sad that this mission is ended, we are nevertheless happy to reflect on the great success of Venus Express as part of ESA’s planetary science programme and are confident that its data will remain important legacy for quite some time to come,” says Martin Kessler, Head of ESA Science Operations.

“The mission has continued for much longer than its planned lifetime and it will now soon go out in a blaze of glory.”

“Venus Express was an important element of the scientific programme of ESA and, even though mission operations are ending, the planetary science community worldwide will continue to benefit from more than eight years of Venus Express data and major discoveries which foster the knowledge of terrestrial planets and their evolution,” says Alvaro Giménez, ESA’s Director of Science and Robotic Exploration.

Notes for Editors:

Summary of the first science results from the aerobraking campaign: http://sci.esa.int/venus-express/54915-venturing-into-the-upper-atmosphere-of-venus/

Eight mission highlights for eight years in orbit – read more about key mission discoveries:

Shape-shifting polar vortices: http://sci.esa.int/venus-express/54062-1-shape-shifting-polar-vortices/

Recent volcanism?: http://sci.esa.int/venus-express/54063-2-recent-volcanism/

Spinning Venus is slowing down: http://sci.esa.int/venus-express/54064-3-spinning-venus-is-slowing-down/

Super-rotation is speeding up: http://sci.esa.int/venus-express/54065-4-super-rotation-is-speeding-up/

Snow on Venus?: http://sci.esa.int/venus-express/54066-5-snow-on-venus/

Ozone layer: http://sci.esa.int/venus-express/54067-6-ozone-layer/

Water loss: http://sci.esa.int/venus-express/54068-7-water-loss/

A magnetic surprise: http://sci.esa.int/venus-express/54069-8-a-magnetic-surprise/

Images, Text, Credits: ESA/C. Carreau/MPS/DLR/IDA, M. Pérez-Ayúcar & C. Wilson/VIRTIS-VenusX IASF-INAF, Observatoire de Paris (R.Hueso, Univ. Bilbao).

Best regards, Orbiter.ch
Full article
The SpaceX Mars plan

ok so a less facetious post about the new penis-shaped SpaceX rocket which SpaceX intends to eventually use to send a million people to Mars

orbital refuelling huh?

so this video is slightly misleading; Musk’s full presentation (slides) fleshes it out a lot more. this post seems to have ended up a text-based summary of Musk’s presentation.

the idea is to use the ~two year period between launch windows for a Hohmann transfer to Mars to place the spaceship in orbit and then send a series of tankers up to incrementally fill it with propellant. There would be ‘about a thousand’ ships being prepared in orbit for each launch window, which all go to Mars when the launch vehicle arrives.

On arrival at Mars, the ship aerobrakes in the Martian atmosphere and then does a powered landing. Then, the plan is to produce propellant in situ from water and carbon dioxide; Musk argues a cryogenic methane/oxygen mix is the most practical for their mission, and this will be used for all parts of the system instead of more traditional higher-specific-impulse rocket fuels like kerosene and hydrogen. Producing fuel on Mars will allow the interplanetary stage to launch from Mars and return to Earth.

All the parts of the system are supposed to be reusable. The booster especially is supposed to have about 1000 uses, the fuel tanker second stage about 100, and the interstellar ship about 12.

The system is currently being designed to carry about 100 people + supplies to Mars on each trip. Musk suggests in the video that they might increase it to about 200 people per trip; he’s estimated (somehow) that a self-sustaining ‘civilisation’ on Mars would require about a million people, which is 10,000 trips on this design. He says he estimates transporting that many people will take 20-50 Mars rendezvous, so about 40-100 years.

He says their launch system will be made of an ‘advanced carbon fiber’ and briefly discusses technical limitations - he says carbon fiber tech has only recently reached the point where they’d be able to store cryogenic fuels without leakage, and prior to that they’d have to have a tank liner.

He talks about a technique called “autogenous pressurisation” where they “gasify the fuel and oxygen through heat exchangers in the engine and use that to pressurise the tanks”. He says this is simpler than Falcon 9′s system of helium and nitrogen pressurisation, and does not require as many substances. To light the engine, they would use spark ignition rather than the ‘complicated’ ignition fuel used in Falcon 9.

SpaceX’s launch system is supposed to have a payload of 550 tonnes to LEO in “expendable mode” and about 300 tonnes in “reusable mode” (compared to the Saturn V’s 135 tonnes as the heaviest lift possible previously).

I’m not sure why the lift-off thrusts are listed in tons-force, and the difference between short and long tons is confusing. Wikipedia lists the first stage thrust of the Saturn V as 35,100kN, and scaling that up with the numbers listed suggests the first stage thrust of the SpaceX Mars vehicle will be 127800kN, consistent with the value shown in the video.

If these claims hold true, this would be a vastly more efficient rocket than the Saturn V in terms of comparison of size to lift capability.

Of course, this design has never flown, so take those numbers with a grain of salt. (Don’t forget how the space shuttle was supposed to fly so much more often…)

Musk says their initial launch site will be the Saturn V’s Pad 39A, which SpaceX is already using for their Falcon series. He says they originally “somewhat oversized” the Saturn V launch pad, so they can launch a bigger ship. He also says they’ll add other launch sites such as the South coast of Texas.

Musk says the ‘Raptor’ engine they’re creating will have the highest chamber pressure and probably highest thrust-to-weight ratio of any engine ever built. In case you want to do calculations with the rocket equation, the specific impulse of 382s in vacuum translates to an effective exhaust velocity of 3750m/s.

(This is lower than the space shuttle‘s main engines and the Saturn V’s second stage in vacuum, so it will use more fuel mass to produce the same change in velocity as one of those ships.)

Musk says he’s confident they can get within a few seconds of 382s, maybe even exceed it.

It’s a full-flow staged combustion cycle. Wikipedia says of such designs:

Full-flow staged combustion (FFSC) is a variation on the staged combustion cycle which uses both an oxidizer-rich and fuel-rich preburner, allowing use of the full flow of both propellants to power the turbines.[4] The fuel turbopump is driven by the fuel-rich preburner, while the oxidizer-rich preburner drives the oxidizer turbopump.[4] This eliminates the need for an interpropellant turbine seal normally required to separate oxidizer-rich gas from the fuel turbopump or fuel-rich gas from the oxidizer turbopump.[5] The increased mass flow from FFSC allows both turbines to run cooler and at lower pressure, leading to a longer engine life and higher reliability. Up to 25 flights were anticipated for one particular engine design studied by the DLR in the frame of the SpaceLiner project.[4]

Since the use of both fuel and oxidizer preburners results in full gasification of each propellant before entering the combustion chamber, FFSC engines are sometimes called gas-gas engines.[5] Full gasification of components leads to faster chemical reactions in the combustion chamber.

According to Elon Musk’s twitter, they fired the Raptor for the first time a couple of days ago.

Musk said in the video that loading the fuels close to their freezing point, instead of close to boiling, increases the density of fuel passing through the rocket and brings several other advantages such as reducing cavitation risk and making it easier to feed the turbopump at high pressure.

(I can’t really say much about this because I don’t know much about the details of rocket engine design.)

The first stage booster should give the spaceship around 8650km/h (2.4km/s), which is about a third of the tangential velocity needed for LEO. Only about 7% of the propellant of the booster wiill be used for returning to the launch pad and landing. Only a third of the LEO velocity doesn’t sound like much, but it has to lift the fuel to get the rest of the way. Fuel spent early on in the mission gets less delta-v than fuel spent later.

The booster will use 42 Raptor engines. Musk compared it to their Falcon 9 which used nine engines, and their soon to launch Falcon Heavy which will have 27.

Of the 42 engines, only the central 7 engines will gimbal for maneuvering, and the rest will be fixed. This allowed them to pack more engines. Musk says it’s designed to be redundant against the loss of multiple engines.

This is the capsule which goes from LEO to Mars. There is a pressurised section at the front, then unpressurised cargo (’really flat-packed’), and finally the tanks of liquid oxygen and methane. Musk says the oxygen tank is the hardest part of the structure to engineer, and talks about some of the challenges.

We can, incidentally, use the rocket equation and the specific impulse of the Raptor vacuum engine to calculate the total delta-v of this vehicle once fully fueled up in orbit, with no cargo. $$\Delta v = v_e \log \frac{M_i}{M_f} = 3750\mathrm{ms^{-1}}\log \frac{2100\mathrm{t}}{150\mathrm{t}}=9886\mathrm{ms^{-1}}$$

This is a fascinating graph that Musk unfortunately only briefly skims over in the presentation. It shows the relationship between the payload mass - people, cargo etc. - and the total available delta-v.

The horizontal axis shows the total payload mass, and the vertical axis shows the delta-v available with this payload. According to info next to the graph, a trans-Mars insertion takes about 6km/s of delta-v. The white line is the total delta-v available for the mission. The greyish region just beneath it shows how much delta-v is required for de-orbiting and powered landing on Mars, which depends on the mass of the payload.

The darker grey region shows, on the horizontal axis, a range of possible payloads, and on the vertical axis, the corresponding range in delta-v for the mission, taking into account the overhead reserved for landing on Mars. That said, if the trans-Mars insertion costs 6km/s, I don’t really understand why a range of delta-vs of 4-6km/s is shown on this graph. Unless some of the launch windows are cheaper? That could be it.

The aerobraking plan is apparently based on their Dragon heatshields and the aerodynamic lift of the capsule. Mars entry speed is going to be 8.5km/s and Earth around 12.5km/s. Musk talks briefly about how their ‘phenolic impregnated carbon ablater” is being developed on Dragon. He claims that they will eventually be able to have many flights without refurbishment.

At 1:02:09 he shows a video of a flythrough of the inside of the capsule and insists it will be “really fun” to increase appeal of flying to Mars. (Not really addressed is how fun it is to labour to build a methane production plant out of nothing in a hostile, freezing environment).

After that, Musk talks about the plan for methane and oxygen production on Mars. He wants to use the Sabatier reaction, and says both water ice and carbon dioxide are abundant on Mars, so the main problem will be the energy source. He vaguely suggests a ‘large field of solar panels’ could do it.

He then goes on to talk about cost. Basically the idea is that, because everything is heavily re-used, the average cost per launch goes down and the idea is that “anyone” who wants to go to Mars could (based on, earlier in the presentation, the median cost of an American house). Nevermind that a very large proportion of people will never be able to afford a median American house? He gives a figure of ‘cost per ton to mars’ of less than $140,000, and suggests the cost of moving to Mars ultimately could drop below $100,000. I guess some people might be able to afford that.

“Obviously it’s going to be a challenge to fund this whole endeavour” you don’t say, Elon…

He says they expect to make a “pretty decent net cashflow” from launching satellites (when they don’t blow up) and lifting stuff to the ISS. He also says there are “a lot of people in the private sector interested in helping to fund a base on Mars” (good idea, comrade Elon. Send the bourgeois to Mars, expropriate their resources, and make them work to make our space colonies!) and also governments. He says “ultimately this will be a huge public-private partnership” and says some rather questionable things about history (“that’s how the United States was founded, a public-private partnership”… and a whole lot of slavery and genocide.)

He briefly mentions his own wealth to say “the main reason I’m personally accumulating assets is to fund this”. Well, when capital drains me dry, at least I’ll know some of it’s going to Mars?

Anyway the rest of the presentation is questionable history and Elon Musk patting himself on the back for SpaceX, followed by a Q&A I haven’t watched yet. He said he created SpaceX is because the trend in spaceship design seemed to be less and less powerful launch vehicles and he thought there needed to be a “new entrant into the space arena” with “a strong ideological motivation” so that people could go “be a spacefaring civilisation and be out there among the stars”. I guess he’s definitely committed to his ideology, but it sure helps to be rich.

On some level I feel sad that the first people to land on Mars could be doing so in the name of a hyper-wealthy capitalist like Elon Musk, but then it’s not like imperialist posturing and getting one over on the Soviet Union was much of a better reason to go to the Moon. And like, if we do get to Mars, that’s exciting whoever’s launched the rocket I guess?

@erin-space-goat had some good points:

i just generally feel like even if this isnt a PR stunt all this effort would be better and more ethically diverted to developing a viable near term rotational gravity habitat and mining asteroids

if the thing depressurizes people are gonna die anyway

and at least spintowns dont have to worry about dust storms

and if the whole gravity balloon thing actually works, the possibilities scale a lot more interestingly

The rocket design seems very well thought through, and given what SpaceX has done so far, I’m willing to believe they could build a rocket with the capabilities described. The broader mission plan - building a thousand of these ships, sending a million volunteers to Mars, setting up a massive scale propellant plant on the other end - seems rather more questionable.

In terms of timescale, Elon Musk gives a very ambitious one: development of the booster in ‘the ten year timeframe’ along with suborbital testing (he talks about the possibility of selling extremely rapid cargo transport), and simultaneously smaller ‘Red Dragon’ missions using their Dragon 2 powered landing, carrying three or four tons for the first few Mars launch windows, and the actual Mars launches with the above scheme in the early 2020s. No doubt this will slip.

The final part of the video shows things they’ve already built: the first tests of the Raptor engine and the first prototype of the huge carbon fibre tank for liquid oxygen. Apparently the initial tests are promising.

Stuff from the Q&A:

  • the booster and capsule would probably be made across multiple US states, with final assembly at launch complex 39A as the rocket is too big to transport on roads.
  • asked about sanitation on Mars, he said the main issue is not water but energy; he talked about solar and nuclear
  • asked about how to select the first people to go to Mars, he highlighted the high risk of fatality in the first Mars missions, and said candidates would be asked if they’re prepared to die. then he said the main thing is to make a “self-sustaining civilisation” on Mars as fast as possible, different from Apollo, and it wouldn’t be so important who the first people to land would be. He starts talking about x-risk but then also about the ‘sense of adventure’.
  • someone asks if they can give him a comic book, that was awkward
  • asked about radiation risk en route and habitat design, he said that the radiation en route is not deadly; that there would be some slight increased risk of cancer but it’s ‘relatively minor’. He does say shielding would be needed if there’s a solar flare, and this would be handled by pointing the rear of the rocket at the sun and clustering around a water column. On Mars he suggests an artifical magnetic field could be made to protect from radiation.
    • He says that SpaceX is just the transport system, and they’re not really addressing the transport system but would leave that to the people who are going to Mars. He refers to ‘enterpeneurship and talent’ and compares it to the Union-Pacific Railway in California because of course he does.
  • someone challenged him on only hiring people from the US. he says that US government regulations prevent people with normal work visas working on rockets without special permission, so it’s out of his hands. he says this is ‘not a wise policy’ for the US but it’s illegal for them to hire people without a green card.
  • someone from funnyordie.com made a really shitty joke about the ‘most expendable human’. Elon managed to salvage it by saying it’s important that people have the option of returning, and they’ll be returning the spaceship anyway.
  • some question about how to encourage people to go to Mars and a bunch of rhetoric. shit about “frontiers” because recalling genocide is definitely where we want to look for our metaphors for space travel.
  • someone asks about how much training the Martian astronauts will need. Elon says ‘a few days training maybe’. sounds… optimistic.
  • currently <5% of the company is working on this, ‘a few tens of millions of dollars’. he says after the final version of Falcon 9 and Dragon 2, they’ll apply more and more resources to the interplanetary system, and they’ll go up to spending more like two-three hundred million dollars per year, which he calls a small part of the overall cost. he estimates it will cost on the order of ten billion dollars before it starts making money back
  • asked if he wants to go to Mars himself, he says yes, but he’d want to make sure there’s a good succession plan so the mission of the company continue if he dies. he says his biggest fear is that if he died, investors would take over who want to maximise the profit and not go to Mars.
  • asked about interstellar travel, he vaguely mentions antimatter as the best way (it’s true that antimatter is the only hope for the Isp you need but good luck making any), but says it’s a long way even to Proxima Centauri. he says once a base on Mars has been established there will be a ‘forcing function’ improving space transportation.
  • asked about a ‘cycler’ - a spaceship on a trajectory that takes it regularly between Earth and Mars - he said their calculations showed that landing on Mars and returning was more cost-effective if the spaceship could be retrieved quickly. he says this might change on the future.
  • he wants to name the first ship to go to Mars Heart of Gold after h2g2.
  • asked about whether people will launch with the capsule, he says it depends how long it takes to fuel up the ship. if it’s a few weeks, people would go up immediately, if it takes a year, there would be a mission to put crew on board
  • asked about NASA’s own Mars plans, he says “it’s good to have multiple irons in the fire” so get your Vriska jokes ready. he doesn’t want SpaceX to be the only company building “architectures like this”, and wanted to encourage governments and companies to build similar systems.
  • he may or may not be the first person on Mars, he says there are “pros and cons” and he’d like to see his kids grow up.

ok phew well that ended up longer than I planned, that’s basically everything that guy said anyway.