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#20
by
Robotbeat
on 20 Oct, 2011 03:27
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For long duration missions just build the Nautilus
I agree for a long mission Nautilus-X is probably the best option.
Now this would be a good starting point to work towards Nautilus sorta like Gemini lead to Apollo.
Start with easier missions such as close NEOs six month mission time and sprint class Mars missions and Venus flybys.
Nautilus X is probably too massive. It'd be quite limited in what sort of missions it could do with a reasonable sized chemical EDS. And the centrifuge they showed probably has a whole host of technical issues just waiting to rear their heads (not that they couldn't be solved, but it'd be difficult). Something built out of more ISS or Space Station Freedom-sized chunks (at least for the core) would probably be better, since it'd allow earlier and cheaper access to more destinations and more delta-v for the same EDS.
The Deep Space Habitat needs to be right-sized in order to ever get off the ground, just like the Apollo mission stack was. It'll have to go through a very large delta-v, so you have to be very frugal with mass, more than you normally would for something in LEO.
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#21
by
Khadgars
on 20 Oct, 2011 03:36
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For long duration missions just build the Nautilus
I agree for a long mission Nautilus-X is probably the best option.
Now this would be a good starting point to work towards Nautilus sorta like Gemini lead to Apollo.
Start with easier missions such as close NEOs six month mission time and sprint class Mars missions and Venus flybys.
Nautilus X is probably too massive. It'd be quite limited in what sort of missions it could do with a reasonable sized chemical EDS. And the centrifuge they showed probably has a whole host of technical issues just waiting to rear their heads (not that they couldn't be solved, but it'd be difficult). Something built out of more ISS or Space Station Freedom-sized chunks (at least for the core) would probably be better, since it'd allow earlier and cheaper access to more destinations and more delta-v for the same EDS.
The Deep Space Habitat needs to be right-sized in order to ever get off the ground, just like the Apollo mission stack was. It'll have to go through a very large delta-v, so you have to be very frugal with mass, more than you normally would for something in LEO.
Exactly, thats why I brought up stacking bunch of ATVs together. Seems (in my limited knowledge) like the most direct path forward for NEO and Mars sprint missions while adding another partner into the fold.
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#22
by
Patchouli
on 20 Oct, 2011 03:45
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The BA-330 already is close that what you'd need for a sprint class mission I think it would be a good starting point.
Take that and figure out what changes would be needed for deep space.
Unlike an ISS module it is a fully self contained space station.
It's only 25,000kg you wouldn't even need depots though I'd get depot technology down before even attempting a Mars mission.
A lot of the same technology needed for depots is needed to keep the propellant for the return trip.
Plus it frees the EDS max fueled mass from the LEO payload limits of the LV.
For long stay missions you're pretty much driven to a Zurbin Mars direct or Nautilus-X architecture depending where you're planning on waiting for the next alignment.
Mars surface is easier in some ways as you don't need fully closed loop life support as there is ice,soil, and atmosphere to be used.
Demos and Phobos can provide some volatiles as well but you'll be processing it in near zero g.
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#23
by
Robotbeat
on 20 Oct, 2011 03:45
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ATVs have about half as much pressurized volume for about the same mass as other (ISS) modules have. Not a very efficient way to provide livable space.
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#24
by
A_M_Swallow
on 20 Oct, 2011 04:28
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The BA-330 already is close that what you'd need for a sprint class mission I think it would be a good starting point.
Take that and figure out what changes would be needed for deep space.
Unlike an ISS module it is a fully self contained space station.
It's only 25,000kg you wouldn't even need depots though I'd get depot technology down before even attempting a Mars mission.
{snip}
A lot of the facilities of a spacestation can be tested for several years unmanned. These include temperature control, electrical power generation and ensuring that it stays air tight. The rest of the life support and hygiene can wait for the people to arrive.
An Atlas V or Delta IV Heavy can lift a BA-330 to LEO. Some sort of upper stage would be needed to lift it to high Earth orbit. This stage could use a chemical thruster or SEP.
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#25
by
Jason1701
on 20 Oct, 2011 05:06
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For long duration missions just build the Nautilus
I agree for a long mission Nautilus-X is probably the best option.
Now this would be a good starting point to work towards Nautilus sorta like Gemini lead to Apollo.
Start with easier missions such as close NEOs six month mission time and sprint class Mars missions and Venus flybys.
Nautilus X is probably too massive. It'd be quite limited in what sort of missions it could do with a reasonable sized chemical EDS. And the centrifuge they showed probably has a whole host of technical issues just waiting to rear their heads (not that they couldn't be solved, but it'd be difficult). Something built out of more ISS or Space Station Freedom-sized chunks (at least for the core) would probably be better, since it'd allow earlier and cheaper access to more destinations and more delta-v for the same EDS.
The Deep Space Habitat needs to be right-sized in order to ever get off the ground, just like the Apollo mission stack was. It'll have to go through a very large delta-v, so you have to be very frugal with mass, more than you normally would for something in LEO.
Exactly, thats why I brought up stacking bunch of ATVs together. Seems (in my limited knowledge) like the most direct path forward for NEO and Mars sprint missions while adding another partner into the fold.
A bunch of stacked ATVs are way heavier than one inflatable with the same volume.
BA-330 for DSH!!
Swallow: Falcon Heavy could launch BA-330 to HEO.
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#26
by
Khadgars
on 20 Oct, 2011 05:28
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For long duration missions just build the Nautilus
I agree for a long mission Nautilus-X is probably the best option.
Now this would be a good starting point to work towards Nautilus sorta like Gemini lead to Apollo.
Start with easier missions such as close NEOs six month mission time and sprint class Mars missions and Venus flybys.
Nautilus X is probably too massive. It'd be quite limited in what sort of missions it could do with a reasonable sized chemical EDS. And the centrifuge they showed probably has a whole host of technical issues just waiting to rear their heads (not that they couldn't be solved, but it'd be difficult). Something built out of more ISS or Space Station Freedom-sized chunks (at least for the core) would probably be better, since it'd allow earlier and cheaper access to more destinations and more delta-v for the same EDS.
The Deep Space Habitat needs to be right-sized in order to ever get off the ground, just like the Apollo mission stack was. It'll have to go through a very large delta-v, so you have to be very frugal with mass, more than you normally would for something in LEO.
Exactly, thats why I brought up stacking bunch of ATVs together. Seems (in my limited knowledge) like the most direct path forward for NEO and Mars sprint missions while adding another partner into the fold.
A bunch of stacked ATVs are way heavier than one inflatable with the same volume.
BA-330 for DSH!!
Swallow: Falcon Heavy could launch BA-330 to HEO.
Ya I understand it's not the most efficient hab, but creating a DSH or BA-330 is far from reality at this point. Just looking at things that will work. But I guess we wouldn't really need one until we're going to Mars any way.
What does a mission to a NEO look like any way, similar to lunar?
Edit: ah from one of Chris's articles it looks like two Orions, MMSEV and DSH. Seems like an awful lot still needs to be developed before we can even attempt NEO. Perhaps thats the reason for more lunar emphasis as of late?
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#27
by
clongton
on 20 Oct, 2011 10:05
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For long duration missions just build the Nautilus-X.
I agree for a long mission Nautilus-X is probably the best option.
Now this would be a good starting point to work towards Nautilus sorta like Gemini lead to Apollo.
Start with easier missions such as close NEOs six month mission time and sprint class Mars missions and Venus flybys.
Nautilus X is probably too massive.
I disagree. It's not big enough. It needs to be at least double that size.
This needs to be a general purpose deep space vehicle, not a mission specific design. Designing a spacecraft for a specific mission is something we have to get over. That was fine when our capabilities were extremely limited. You *had* to do it that way to make sure you could do the mission. But our capabilities have grown well beyond that now. We are now setting out on a path of general exploration, going to many different destinations in several different places in the solar system. We need a general purpose spacecraft design that can handle a large crew, perhaps as many as 12. And we need a small fleet of them.
While the trucking industry still design specific-purpose trucks, their largest truck production facilities are in the long-haul general purpose heavy vehicles, because they don't have any idea what the people will use them for except for long haul heavy trucking. NASA needs to *begin* to adopt the same mindset. We will always have a need for small one-of spacecraft, but NASA's main deep space spacecraft future lies in fleets of general purpose heavy haulers. Nautilus-X is a good place to start but will prove to be too small for general purpose exploration. It's time to put the harbor sloop away and move to the ocean-going sailing ship.
And just to stir this pot up some more it's also time to get away from chemical propulsion for these deep space designs. Go VASIMR or NTR for the MPS.
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#28
by
Robotbeat
on 20 Oct, 2011 14:21
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A modular approach using ISS-like modules means you don't have to design everything all over again for each mission.
I agree going with high-Isp propulsion (especially electric propulsion) would remove a lot of mass constraints, but I'm pretty sure that designing a spacecraft for 12 occupants to deep space is getting a little ahead of ourselves. It's not needed even when we have a Martian base, only once we want to start a settlement.
Designing it for 12 people would mean it's far less likely to ever happen. It'd push off the first NEA mission (and the first Mars mission) considerably to the right. The closer to the left in schedule a mission is, the greater chance it has of avoiding cancelation (and cost over-runs, etc). We shouldn't need a spacecraft bigger than ISS just to go to a NEA. With a smaller, 60mT or less exploration stack (Mars version of Orion, SEV, DSH), a 260mT CPS could launch it to multiple different NEAs, and if staged from HEO or EML1 or EML2, it would have enough delta-v to push that whole stack through the 8+km/s needed for a short-stay Mars mission. With a 150-200mT exploration stack, you'd need a far bigger CPS (quite possibly requiring orbital assembly) or high-isp propulsion would be on the critical path (and you'd need a much larger high-Isp propulsion stage than for the much smaller 50-60mT 4 person exploration stack).
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#29
by
peter-b
on 20 Oct, 2011 19:41
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There are two points I want to make.
Rotating sections
Although I agree that rotating sections to provide simulated gravity are technically challenging, I think they're more-or-less essential for long-duration spacecraft or space stations. There are two main reasons for this.
Firstly, contribution to crew health. If the crew can sleep and spend much of their working time in a macro gravity environment (say, Mars-equivalent or higher), then muscle and bone mass loss will be reduced. Now, admittedly we don't yet have models for how much that loss will be reduced by, but that's partly because no-one's done the experiments...
Secondly, reduction in consumables and trash generation. If you have a macro gravity environment, it's much easier to e.g. wash and dry clothes and eating utensils, cook with bulk ingredients rather than needing everything in individual packages, etc.
Propulsion and power
Propulsion is a major challenge. It's desirable to have very high Isp, to maximise the mass fraction of your spacecraft, but the power consumption of the spacecraft is important to consider as well. The ISS requires enormous solar arrays to function, and it doesn't have an huge, constant propulsion power requirement.
There are a lot of trade-offs to be made between specific impulse and specific mass, and I don't think anyone's found the "right answer" yet. VASIMR seems to be an unhappy compromise to me; it scales well, but it has significantly lower Isp and lower power efficiency (~60%) than other electric propulsion systems (e.g. HiPEP, which manages ~80%).
Studies done by Ad Astra on VASIMR-based Mars mission designs seem to assume power supplies that achieve 4 kW/kg, and I'm pretty certain that can't be achieved with solar power in Mars orbit; it seems like either we need to have a breakthrough on extremely lightweight solar cells and structures for microgravity/low gravity applications, or we need to actually get on and build fission reactors for space applications...
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#30
by
clongton
on 20 Oct, 2011 20:03
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Studies done by Ad Astra on VASIMR-based Mars mission designs seem to assume power supplies that achieve 4 kW/kg, and I'm pretty certain that can't be achieved with solar power in Mars orbit; it seems like either we need to have a breakthrough on extremely lightweight solar cells and structures for microgravity/low gravity applications, or we need to actually get on and build fission reactors for space applications...
Which is why I mentioned VASMIR and NTR in the same sentence. I believe we need to have all our electrical power generation done by a nuclear reactor of some type, and use that to power the VASMIR during cruise phase, taking advantage of the high isp and the rapid transit times that makes possible. But do it in such a way that we also have on-demand high thrust NTR for rapid acceleration or deceleration; i.e., entering or leaving orbit and emergency rapid collision avoidance maneuvering.
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#31
by
manboy
on 20 Oct, 2011 20:30
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For long duration missions just build the Nautilus-X.
I agree for a long mission Nautilus-X is probably the best option.
Now this would be a good starting point to work towards Nautilus sorta like Gemini lead to Apollo.
Start with easier missions such as close NEOs six month mission time and sprint class Mars missions and Venus flybys.
Nautilus X is probably too massive.
I disagree. It's not big enough. It needs to be at least double that size.
This needs to be a general purpose deep space vehicle, not a mission specific design. Designing a spacecraft for a specific mission is something we have to get over. That was fine when our capabilities were extremely limited. You *had* to do it that way to make sure you could do the mission. But our capabilities have grown well beyond that now. We are now setting out on a path of general exploration, going to many different destinations in several different places in the solar system. We need a general purpose spacecraft design that can handle a large crew, perhaps as many as 12. And we need a small fleet of them.
Seems like you're looking at a different budget than everyone else.
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#32
by
A_M_Swallow
on 20 Oct, 2011 20:39
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A bunch of stacked ATVs are way heavier than one inflatable with the same volume.
BA-330 for DSH!!
Swallow: Falcon Heavy could launch BA-330 to HEO.
KISS.
When both the BA-330 and Falcon Heavy have been flow separately marrying them will probably be a good idea.
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#33
by
A_M_Swallow
on 20 Oct, 2011 20:44
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Studies done by Ad Astra on VASIMR-based Mars mission designs seem to assume power supplies that achieve 4 kW/kg, and I'm pretty certain that can't be achieved with solar power in Mars orbit; it seems like either we need to have a breakthrough on extremely lightweight solar cells and structures for microgravity/low gravity applications, or we need to actually get on and build fission reactors for space applications...
Which is why I mentioned VASMIR and NTR in the same sentence. I believe we need to have all our electrical power generation done by a nuclear reactor of some type, and use that to power the VASMIR during cruise phase, taking advantage of the high isp and the rapid transit times that makes possible. But do it in such a way that we also have on-demand high thrust NTR for rapid acceleration or deceleration; i.e., entering or leaving orbit and emergency rapid collision avoidance maneuvering.
Small delta-V, high thrust with space storable propellant. Is the parking thrusting on the SEP best done by NTR or a methane thruster?
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#34
by
clongton
on 20 Oct, 2011 20:47
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Seems like you're looking at a different budget than everyone else.
To quote a certain well-known Senate Staffer: "It's only money".
Don't let the doom-sayers running amuck inside the beltway fool you. There is more money in this country than you can shake a stick at. If you go into Congress and ask for $20 billion, you'll get $12-$15. If you ask for $30 billion you'll get $20 to $25 and so forth. If this kind of effort required $100 billion then you go in and ask for it. You won't get it all but you will get most of it - guarenteed.
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#35
by
clongton
on 20 Oct, 2011 20:50
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Studies done by Ad Astra on VASIMR-based Mars mission designs seem to assume power supplies that achieve 4 kW/kg, and I'm pretty certain that can't be achieved with solar power in Mars orbit; it seems like either we need to have a breakthrough on extremely lightweight solar cells and structures for microgravity/low gravity applications, or we need to actually get on and build fission reactors for space applications...
Which is why I mentioned VASMIR and NTR in the same sentence. I believe we need to have all our electrical power generation done by a nuclear reactor of some type, and use that to power the VASMIR during cruise phase, taking advantage of the high isp and the rapid transit times that makes possible. But do it in such a way that we also have on-demand high thrust NTR for rapid acceleration or deceleration; i.e., entering or leaving orbit and emergency rapid collision avoidance maneuvering.
Small delta-V, high thrust with space storable propellant. Is the parking thrusting on the SEP best done by NTR or a methane thruster?
I'd use the reactor in NTR mode. It is *deeply* throttlable.
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#36
by
Solman
on 20 Oct, 2011 21:13
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Studies done by Ad Astra on VASIMR-based Mars mission designs seem to assume power supplies that achieve 4 kW/kg, and I'm pretty certain that can't be achieved with solar power in Mars orbit; it seems like either we need to have a breakthrough on extremely lightweight solar cells and structures for microgravity/low gravity applications, or we need to actually get on and build fission reactors for space applications...
Which is why I mentioned VASMIR and NTR in the same sentence. I believe we need to have all our electrical power generation done by a nuclear reactor of some type, and use that to power the VASMIR during cruise phase, taking advantage of the high isp and the rapid transit times that makes possible. But do it in such a way that we also have on-demand high thrust NTR for rapid acceleration or deceleration; i.e., entering or leaving orbit and emergency rapid collision avoidance maneuvering.
Another option is to use a large solar concentrator mirror and concentrator type PV. The focused sunlight may be used directly to power a solar thermal rocket for orbit raising to a highly elliptical orbit in a reasonable time v. electric propulsion; and then switch to solar electric after a departure thrust to just over escape velocity. Oxygen injection is also a possibility for thrust increase for the departure thrust.
The concentrator can potentially have specific power much higher than a solar cell array although the power is in the form of light not electricity. This means that at the distance of Mars a larger concentrator is required for a concentrator type PV system than at Earth's distance from the Sun, but this concentrator potentially adds much less mass than having a roughly 2.5 times larger solar cell array. A combination of solar thermal and electric can be used to provide a large range of Isp's like VASIMR and both can use lithium effectively as propellant although solar thermal can use almost anything and hydrogen is of course best.
If the Prometheus project is any indication, whatever advantage reactors confer comes at quite a cost! Also isn't there a problem with using a NTR reactor for electric power generation? It certainly is different in design than reactors designed for electric power production.
Steve Mickler
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#37
by
Robotbeat
on 20 Oct, 2011 22:04
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....
Studies done by Ad Astra on VASIMR-based Mars mission designs seem to assume power supplies that achieve 4 kW/kg, and I'm pretty certain that can't be achieved with solar power in Mars orbit...
It actually can:
EDIT:forgot the link!
http://www.spacefuture.com/archive/early_commercial_demonstration_of_space_solar_power_using_ultra_lightweight_arrays.shtml"Manufacturing capability is critical. Ultra-lightweight carbon fiber-reinforced polymer, thin-film solar cell (CFRP TFSC) arrays provide, low payload volume and low payload mass space solar arrays that are the key enabling technology for SPS. The ability to make such solar arrays has been demonstrated at laboratory scale in the form of record power density 4300 W/kg, 9.5% stabilized efficiency AM0 (1357 Standard) 122 W/m2 thin-film solar cells on 6 micron thickness CP1 polyimide superstrates (polymer film towards the light).
In-space conditions offer temperatures which have been shown to self-repair a-Si cells by heat annealing. These same 6 micron thickness a-Si:H TFSC, which are 9.5% efficient under room temperature conditions, are 12.4% efficient and will provide 5950 W/kg and 170 W/m2 under 100oC space heat annealing self-repair conditions. Depositing these TFSC on 2 micron thickness CP1 or CORIN polyimide will reduce the superstrate weight by 2/3 and increase the area per kilogram of the array to approximately 100 m² per kilogram. 100 m² of TFSC that produces 170 Watts/m² predicts bare solar arrays with
power density 17,000 Watts/kilogram."
and
"2007-2008 R&D plans at Welsom includes the deposition TFSC on 2 micron thickness CP1/CORIN. TFSC on 2 microns thickness polyimide superstrates and 15.2% efficient TFSC expected under space conditions of heat annealing and self-repair, predict the manufacture of record power density solar arrays
in excess of 10,000 Watts/kilogram."
(you need ~8000W/kg at Earth to equal ~4000W/kg at Mars, of course)
Now, there are improvements in efficiency all the time. These figures are for ~9-15% efficient cells. Once efficiency improves (and there should be room for considerable improvement in efficiency since it's much lower than state of the art) in a few decades, I wouldn't be surprised if you didn't get 30-45% efficiency, so you could get even higher than 10kW/kg at Earth.
There is a ways to get there, but it seems well within the bounds of possibility (and actually, IKAROS demonstrated recently an equivalent specific power of about ~1kW/kg at 1AU without a lot of attention given to either efficiency or using the very lightest sort of solar array/sail material).
In 20-30 years, 8kW/kg at 1AU is feasible, IMO.
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#38
by
baldusi
on 20 Oct, 2011 22:36
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The VASIMR paper assumed a 12MW power source. At 675W/mē of solar energy density at Mars distance, and assuming an efficiency of 9%, that's an effective energy input of 60.75W/mē. So, you'd need around 200,000mē of effective light gathering surface, i.e. assuming no losses due to light incidence angle. That's roughly a 500m x 500m solar panel or a circle of 520m in diameter. Kind of too big, isn't it?
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#39
by
Robotbeat
on 20 Oct, 2011 23:09
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The VASIMR paper assumed a 12MW power source. At 675W/mē of solar energy density at Mars distance, and assuming an efficiency of 9%, that's an effective energy input of 60.75W/mē. So, you'd need around 200,000mē of effective light gathering surface, i.e. assuming no losses due to light incidence angle. That's roughly a 500m x 500m solar panel or a circle of 520m in diameter. Kind of too big, isn't it?
Why is it too big? Surely you should have plenty of... ahem... space!
