- Dimensions: 4 m diameter at ends, 5 m diameter at Whipple shield body casing, 60 m length (image is not exactly to scale)
- Composition: primarily high-emissivity graffold (folded graphene) scaffolding, some layering of low absorptivity high emissivity alloy and Whipple shield exterior for anti-laser and kinetic defense
- Dry Mass: roughly 20 tons
- Wet Mass: potential maximum of 40 to 65 tons depending on fuel type used (100 MPa hydrogen or helium isotopes)
- Wingspan: 30 meters per radiator-wing, folds-up to 5 meters
- Thrust/Weight: designed for up to continuous 5 G acceleration, achieved by multi-terawatt ICF drives (number and position depend on configuration)
- Powerplant: 50 MW Brayton Cycle generator with argon working fluid
- Sensors: Frontal and rear IR batteries, radar and skin-incorporated antenna
- Armament: High frequency UV semiconductor laser with 3 turrets, missile loadout, twin spinal coilguns, nuclear exhaust may be used at close range
This is a departure from my regular work towards something more speculative; a true “spacefighter”, a small vessel capable of operating both in space and in an atmosphere. Each one of these is an enormously demanding task on its own, hence the hybrid craft must make a number of compromises to fully operate.
A military vessel first and foremost, the starfighter is not a comfortable ride. Variable thrust and gravity will send the pilot rocking, which the gyroscopic cockpit can only do so much to accommodate, and it has no life support, so he must remain in his space suit at all times. The craft is not meant to hold him for more than a few hours – ideally it is only operated from carriers or planetary bases during skirmishes. That being said, the frontal module can be ejected in case of an emergency, at which solar panels unfurl to provide enough power to operate antenna and coordinate a rescue mission. The starfighter’s minimal design lends to easy conversion to a drone or smart-ship, as this only requires putting a decent computer in place of the cockpit.
In battle, the starfighter serves chiefly as an interceptor or assault craft. As an interceptor, it shoots down incoming missiles and directs fire away from more vital ships. When on the attack, the onboard lasers might not be powerful enough to do significant damage to larger ships, but equipped nukes allow it take down a limited number of opponents of any size. Some militaries even prefer them to capital ships, as many can be built for the same cost as a larger vessel and each loss is less of a hit to the fleet, yet in their numbers they are harder to take down.
Exacting detail of ship systems and functioning is available if desired. I must thank the
Atomic Rockets website for its invaluable contributions to the above, as well as NASA for specifics of supersonic flight and surface-to-orbit craft. I hope it merits both their seals of approval.
Now, I am no rocket scientist, nor do I work at Boeing, but I do have a better-than average understanding of how planes work, including supersonic flight.
First of all, I must ask what in the world your craft does in the atmosphere- It does not seem to have SSTO capabilities, or Air to Ground or Air to Air weaponry. The ability of it to go in atmosphere does not seem to have an purpose. but, I am not yet done with this design, as I believe that there are several things on it that could be vastly improved to give it a fighting chance at surviving being bombarded by air particles.
1- lets start easy(ish). Those wings.
1a. I would make them 2 piece wings. actually, I would make them one piece. At the speeds this thing is going, there is simply no way they could reasonable be made out of so many segments. the illustration seems to show them sliding next to each other, but this would not make much sense. the best possible route would be to have them fold like that of an F-18, if you want to save space. I would implore you to simply forgo the hinges and instead go for a stronger wing, but I do not know how important saving space is to the carrier spacecraft.
1b. I would make sure that your leading edges are made of the most heat resistant material you can afford. At the speeds this thing will be going, they are going to get really, really hot.
1c. this thing needs a vertical stabilizer. you don't want to deal with the pain in the rear controlling Yaw is without one. it's doable, but it will add a lot of complexity to your wings, which you really already want as simple as possible. also, something tells me that using spoilers at hypersonic speeds is not going to be a good time.
1d. Your control surfaces do not seem to be labeled, but I would use a split elevon like the space shuttle. you will be going comparable speeds, and that is the fastest manned aircraft we have yet made.
2- Fuselage Design. I smell not a whiff of area ruling.
2a. Area ruling is an advanced technique of slowly increasing an aircraft's cross section gradually. this helps reduce the drag caused by the weird effects of going over Mach 0.8. Your sharp bump where your sensors are is particularly gruesome. easy fix though- stick em in the nose!
2b. tail/ nose design- as I state later, drop the nose laser. your entire nose looks very un-aerodynamic.
3- In-Atmosphere Propulsion
3a.- taking off- I would highly advise against using an SSTO design- this is an interceptor- put it on an SRB and get it up there!
3b.- air breathing engines- throw out the turbojets- those are just extra weight. I would use a pair of ramjets, buried in the middle of the wings. To take off, use a disposable rocket.
4- armament- the current weapons work nice in space, but...
4a.- drop that nose laser! it will get melted by flying in atmosphere! replace it with a nice, sleek, heat resistant nose. Put your sensors in that.
4b.- you might want some in- atmosphere weapons. You likely want just a handful of radar guided missiles, in weapon bays like those of the F-22/F-35. these will be heavy, as they will require being strong to be opened at the speeds we are talking. I would make they bays big enough to fit some bombs, too.
Thats about it, fix that and you should have a very viable aircraft!
As initially envisioned nearly three years ago, the Exacting was meant to be a physically viable version of the pop-cultural starfighter, a one-manned supership capable of operating in space or in atmosphere, so I tried to give it all those capabilities. Though I do think there is some room for transatmospheric craft capable of operating in both realms, I will freely admit that having separate aerial and spatial platforms is both easier to achieve and more practical, and most likely the greatest need would arise simply from granting the ability to tend to ships on the ground and still get them into space without much inbetween.
Certainly, there isn’t as much information on the aerial performance, mostly because I did not have much luck in finding the data, or at least something I could put to numbers, so I’d agree that this aspect is the weakest. But I should say that some of those points are already counted for, or were compromises:
1a. I was trying to kill two birds with one stone by getting the extended surface area of the radiators to do double duty and also serve as wings, which is why it’s a delta-wing design. Were this a purely atmospheric craft, there’d have been no need for radiators - I’d have just used inlets to take in surrounding air as coolant – and these would have been a single piece. I did consider at the time that it couldn’t be healthy to have such stresses on sliding members, but I needed the radiators to be able to withdraw to reduce cross-section and vulnerable area. That being said, were I to redesign this, I would probably use solid state heat systems in which case getting shot isn’t as big of an issue, and they could afford to be single piece even in space.
1b. Already taken care of; the ship armor is composed largely of graffold (graphene folded to increase its compression strength; certainly the stuff is super-strong in tension, but not so much on this end), which has a melting temperature of 4000 K, and its very high emissivity means that it likely won’t ever get that hot in atmosphere because it’ll be radiating heat out so quickly.
1c. Point taken; it wouldn’t be hard to add either.
1d. It does have elevons, though since, as you pointed out, they’re not labelled, I can understand the dilemma.
2a. I’m not sure what side of the fence to be on here – on the one hand, improving aerodynamics is critical for this ship’s function especially at high speed, but on the other, the taper means the ship needs to be longer to have the same volume and is going to use up more mass as armor due to the greater surface area. Exacting does have the delta-v to spare though...
2b. I’d really rather not drop the nose, because that single laser gets much better coverage than anything else, and unlike the other two, can actually fire ahead. This is actually more critical to the aerial performance than the spatial, since the spacecraft is free to rotate to keep its turrets pointing the right way (not that it isn’t a great idea in space too – it keeps a minimum cross-section towards its target).
3a. If taking off were the only thing we were doing, I’d not bother with turbojets or SRBs; I’d couple it to a lifter (as delta7Xx suggests) or use the ship’s main drive (since this is basically a torchship, at least if I’m not concerned about irradiating the surrounding countryside). Given the tech required just to make the ship’s drive, an independent booster could probably do better than current chemical rockets. But...
3b. The ship’s doing more than just taking off here, it is meant to be able to actually fight in atmosphere (and if all it were doing was taking off into orbit, concessions to aerodynamics and steering would be minimal). It needs to be able to move around for extended periods in air, hence the turbojet/scramjet combination.
4a. I think I dealt with this in 1b and 2b. The sensors definitely need moved though; I’d probably distribute them across the body for better all-around coverage.
4b. In retrospect, I’m really not sure why I never gave the Exacting missiles, which could have also benefitted it in space as well, especially since one of my own arguments for the practicality of starfighters basically revolved around their ubiquitous use. Most likely, I was trying to conserve mass, but that’s something I’d definitely change.
At any rate, I think we can agree that the ship needs work on this front. I’ve also learned a lot about the grittier details of spaceships during my work on Starfighter Inc, and there are some things I’d do differently if I were to make it today. I’ve been procrastinating on making a more grounded Mark 2, but nearly all my design time tends to go to the game rather than my own work...
It’s something for the future. I’ll definitely be taking these into account, PositiveAnion; thank you.
you know, just as one last piece of input, I had a thought about Hybrid vehicles. When making a hybrid, you must look at what is the most limiting of the two vehicular types, and make sure your design fits in that first, and then do the less limiting one.
Take for instance the Terrafugia Transition flying car. the very first flying cars were simply cars with folding wings and a powerplant- very unpractical both to fly and to drive. However, the Transition team realized that the problem is the very phrase "Flying car." A flying car will never be practical, because to make a car fly, will make it unpractical to drive. ut what they made was a road-drivable plane. This simple change in perspective is what made their design successful.
Another example is the LAV. these are armored fighting vehicles that can go in the water, instead of boats that can drive, since the water has less restrictions than do roads.
If you look at the Space Shuttle, or the Buran or the X-37. these are, outwardly, planes that can go to space, not spaceships that can fly.
I totally understand if you don't have time to redesign it- Work takes precedence, as food and paying bills are generally important.
the orion class in it's current form is also very well armed on it's own, (as would likely be any large orion style nuclear pulse jet warship), and i love the idea of arming the orion with nuclear bomb pumped gamma ray lasers that can fire dozens of beams with a single burst. not only would the ship already be carrying the low payload nukes it uses to begin with, but it also could act as a powerful point defense system to deal with enemy fighters such as these (though reloading it would take a while naturally.) and if im not mistaken, the battleship orion had the hanger capacity for approximately 3 space shuttle sized craft, and this thing appears to fit that size scale perfectly.
Thank you for telling me about Atomic Rockets. It looks like a fantastic resource. Unfortunately, it pokes a few holes in some of my ideas.
How much volume would it take to provide life support for about a week?
how long would it take to reach 0.25c if accelerating 5G continuously?
Here are my ballpark estimates on life support size. Take a minimum of 1 m3 for any vessel if it has a crew of less than ten and makes daily commutes, adding another 1-1.5 m3 for every ten people. For a freestyle corvette that might have a crew of 10 off the beaten path for 2 weeks or so, 3.5 m3 (it can reclaim water and oxygen, but at least half of this is stored food). For a medium-sized military or exploratory vessel (a crew of 100 or so travelling for a few months), I’d go with 180 m3. For a space station or colony ship, figure 2000 m3 per every thousand people it’s supposed to hold if it can get food from elsewhere (I’m guessing the station has to hold its own for at least 6 months at a time), 8000 m3 if they have dedicated hydroponics, 16000 m3 if they want occasional station-grown meat, maybe a whole 80000 m3 if they want it regularly. You can get any of these ships to be capable of nearly indefinite cruise time by using edible algae tanks, which add less than a cubic meter in all the former cases, if used as a substitute when stores run out, but if you’re relying solely on them, I’d say the figures become 1 m3, 1.9 m3, 21 m3 and 200 m3. What I based these on, I will explain below.
The Atomic Rockets site has a good page on the matter (here), and I am going to quote some of their figures, but they didn’t really go into dealing with temperature or humidity. However you look at it, how much space the system needs depends on how long you’re away from supply lines. If it’s not long, it’s easier to store whatever you need, but past a few months you’ll want to think about recycling whatever’s available. I should note that even on long voyages, stored food takes so little space relative to tanks and greenhouses that I don’t think the latter pays off unless you have a very large crew, and even on very short voyages, you will still need a decent air scrubber (mostly for CO2 but other trace contaminants too).
I’ll look into those first. Based on NASA figures, a person releases about 1.155 kg of carbon dioxide per day. Current carbon dioxide scrubbers generally involve either binding the gas or reacting it with another compound and hence have limited storage capacity, though NASA has developed regenerative ones that can be made to later release the CO2 allowing continuous use (detailed here). I can’t find figures for the volume, but mass of a unit was given as 15.4 kg, and based on the densities of the other devices given, I imagine volume is around 0.06 m3, possibly quite less than that, this on Skylab meant to take up to 8 crewmembers at most, so that gives us 7.5e-3 m3/person. If you already have greenhouses or tanks big enough to feed the whole crew, then you don’t really need to look into this – they’ll convert enough CO2 on their own – but if not, you could still develop an algal tank on a smaller scale to use as a convertor. I’m going out on a limb here, but Seambiotic states that one gram of algae can convert two grams of CO2 per day, so that would imply that you need 0.578 kg of algae per person, and the highest densities achieved in cultures are about 20 g/L, so that would require 28.9 liters, which I’d bump up to at least 30 L (0.03 m3) to take account of support equipment to keep them from dying. Artificial photosynthetic devices have since been developed with ten times the efficiency and can be made much denser, so I reason you could manage under a liter, maybe as little as half a liter, for the same effect (5e-4 – 1e-3 m3). I should note that either of these will require some extra water for the conversion process (about 0.5 kg, that’s 0.5 L of liquid water per person per day), but since that’s about the mass of water vapor a breathes in that time, you could easily reclaim it with a dehumidifier, and the reduced product is edible too.
Trace contaminant scrubbing is harder to find figures for – these seem to work much like current CO2 scrubbers, but with different catalysts involved. A high air-flow HEPA filter sized 610 x 305 x 35 mm (that’s a volume of 6.5e-3 m3) can filter up to 450 m3/h = 10800 m3/day, while a person inhales some 11000 liters = 11 m3 of air in that time, so that gives 6.62e-6 m3/person. That’s so small you could easily incorporate it into the CO2 scrubber. As for humidity control, this could be managed by a combination of a humidifier (which sprays such small droplets of water they immediately evaporate) and a dehumidifier (which either cools the air enough for water vapor to condense or uses hygroscopic chemicals to capture it). The former is relatively tiny compared to the latter so the second is what I’ll focus on. A highly efficient Phoenix 200 Max is sized 24”-40”-21 3/8” (that’s 0.32 m3) and can remove up to 30 gallons per day, that’s 375 kg/day per cubic meter of machine, or 1.3e-3 m3/person. In practice, I think that volume would be somewhat smaller, because all three scrubbers could use the same fans and ventilation, so you could probably shrink this to 1e-3 m3/person. If you have a greenhouse, boost the dehumidifier to handle plant transpiration, because plants lose almost all the water they take up this way – just how much depends on the plant, and is usually around 0.2-1 kg/day of water per kilo of most crops, up to a horrific 3 kg/day per kilo of rice, which would be anywhere from 4e-4 - 2e-3 - 6e-3 m3/kg of plant, and you’re probably growing several tons of them. (These figures are based on a combination of this page with those on Wikipedia figures).
As for the rest, the simplest answer I could give is this. Atomic Rockets deduced that a 150 man crew on a 90 day voyage where only water is recycled would need some 165 m3 of storage – 80 m3 for food (that’s 2.3 kg per person per day, a goodly portion) and about as much volume for refrigeration (though you could take this away by vacuum packing), 3.5 m3 for oxygen (stored under pressure or cryogenically) and the remaining 1.5 m3 for water. That gives you 0.012 m3 per person per day. If there were no recycling whatsoever, you’d need considerably more volume – according to NASA figures, astronauts use an average of 3 gallons or 12 kg of water per day, which would amount to 162 m3 for the situation described. The average American uses 12 times as much, but I should note that very little of this is used on drinking water. More than half of it goes to clothes and dishwashing as well as toilet-flushing, processes which could be mostly substituted with chemical or mechanical means, and the significant contribution of outdoor use and leaks shouldn’t be an issue here, which should allow us to reduce use to a third that and still live comfortably, for a volume of 648 m3. Basically, if you completely skimped out, you could get by with as little as 6.3e-3 m3 per person per day, and if you wanted to live it up, go up to 0.06 m3 per person per day. In practice these values will be higher for extremely short trips because the storage and distribution structures will take up relatively more room, so take anywhere from 0.2-1 m3 as a minimum value.
Water is partly reclaimed by the dehumidifier, but a lot more can be taken back by cleaning waste water from the sinks and showers via catalytic filters, and converting urine via a combination of distillation and centrifuging. The final product must be disinfected to ensure it’s drinkable, requiring a UV light or possibly chemical treatment and reclamation. I can’t find exact figures for NASA’s Water Processor Assembly ( here), but a ‘refrigerator-sized’ unit (I’d generously guess that’s a 2 m3 box) can recycle 13.2 pounds = 6 kg of water per hour. As this is a preliminary unit, you could probably safely halve or even quarter this for a more advanced version, so make that 288 kg/day from a 0.5 m3 unit. Above we’ve determined daily water use can be anything from 12-48 kg/day per person depending on how thrifty you intend to be, which gives you 0.02-0.08 m3/person.
Food is a tough one, and it gets tougher if you want your passengers to have any variety in their meals. Algae tanks are one thing – from Atomic Rocket, a 6 liter tank will produce enough algae for a person’s dietary needs, that is 6e-3 m3/person – but if you want other plants in your diet or any meat at all, it’s going to get huge, and it’ll need some tending. Hydroponics bays can achieve growths of up to 35 kg/m2, but most annual crops take growing seasons about 4 months long, so that’s nearly 0.3 kg/m2 per day, and you’ll need 7.6 m2/person (for simplicity you can assume that the average crop you intend to grow tops out at 1 meter tall, so this becomes 7.6 m3/person). If you bring livestock aboard for meat, you’ll need quite a bit more, not just for holding pens but to provide a place to slaughter them, cut and clean the meat, and most importantly more space to grow even more plant food for the animals (daily rates are 11 kg/cow, 3.6 kg/pig, 2.25 kg/sheep, 0.11 kg/chicken). Unless you have a really huge ship, chickens are the only ones that might be worth keeping around – for one thing, the hens will constantly provide you food in the form of eggs so long as they’re alive.
For recycling solid waste (feces and garbage), the best option I could find was a microwave incinerator (patent here, with better explanation on functioning here), and elsewhere I’ve found a hospital version described as being 0.2 meters in diameter and 0.9 meters high, for a volume of 0.028 m3. As hospitals may have hundreds or even thousands of employees and patients, this should be sufficient for all but the largest ships.
There is another matter I have yet to look into to, and that’s heat regulation: this can be accomplished by a combination of resistors in the vents with an outer surface that regulates solar absorption (flaps of reflective material fold over absorbent ones) and extensive radiators to dispose of any excess heat, none of which really contribute to volume (for similar reasons I have not gone into radiation shielding – that’s really up to the external coating). That being said, if your living space is very large or located in the center of the ship then cooling becomes a problem, and you will want to look into it. As before, you can either store the heat or deal with it. To store it, you’ll want a coolant to take it up, such as liquid nitrogen. At pressures of 700 atm, the density of nitrogen gas is 815.5 kg/m3, very close to that of its liquid form, and the liquid will take some 250 kJ/kg of heat as it boils and heats up to room temperature, which is to say you’ll need a volume of 4.9e-3 m3/MJ you wish to dispose of, and I’d probably round that up to 5e-3 or even 6e-3 to account for insulation. If you wish to deal with the heat instead, you’ll need a refrigeration system, as it will dispose of the waste heat at a higher temperature that your radiators can more effectively get rid of. The refrigerator will create more waste heat of its own, possibly even more than you’re trying to get rid of, but even this can be made to work out for a big enough temperature difference. As an example, say your radiators run at 600 K, just over twice the heat of your living space (probably 20-25 C, or 293-298 K). The second law of thermodynamics says that at best, a refrigerator has a coefficient of performance of 1/((Thot/Tcold)-1), which is to say it will move that many times as much heat as it creates: in this case, COP = 1, so you create as much heat as you want to get rid of. However, radiators dispose of heat as function of the fourth power of temperature, so by doubling radiator temperature, you’ve improved capability 2^4 = 16-fold, and even with doubled heat you’ll still manage with 1/8th the space. I can’t find figures for the exact volume (because the given volume for commercial refrigerators includes the food storage space), but based on my own refrigerator, which could be made smaller by packing components more tightly, I’d say 0.025 m3/kW is a good figure.
How much heat do you have to get rid of? Each person produces around 0.135 kW, or 11.66 MJ/day. I cannot find decent figures, but the highest power rating I could find for the average home anywhere in the world was around 2 kW (172.8 MJ/day), and the International Space Station ends up converting nearly all its electrical power into heat, so consider that a decent benchmark.
I suspect there will be a few battleships regardless – lasers can still shoot down missiles before they’re in range and such large vessels would have the space and faculties to field a lot of them, especially if their own fighter retinues are on the defensive, so they’re not automatically out of the fight. Moreover, they are large enough to carry infrastructure allowing them to operate independently, where a starfighter would be stranded without a carrier or helpful planet to return to, and they could bear bigger turrets that could launch stronger beams, capable of seriously damaging other craft with no good means of being stopped and even taking down planetary targets. That being said, my feeling is that the technical background briefing in Homeworld made a very good point about the utility of fighter ships: “Time and resources in combat often do not allow the creation and maintenance of a large force of Capital Ships. And we needn’t even bother to analyze the true costs of losing a single large vessel when compared to the attrition a fighter squadron can suffer while still being maintained at combat readiness. Are you aware of the number of Interceptors one can build for the cost of a single Assault Frigate? Now granted, each one packs only a tiny amount of the Frigate’s firepower and certainly cannot survive more than one or two hits from a heavy gun, but I ask you: Exactly how much damage can 75 interceptors do in the time it takes to kill just one of them?” The answer would be quite a bit if you’re willing to use nukes.
At 5 G, getting to 0.25 c would take roughly 17 days and 17 hours – and you would not be comfortable with it at all. Fighter pilots and astronauts are trained to tolerate up to 10 G, but 5 is about as much as the average person can cope with. The only ways to beat this barrier are to stay in liquid pods to brace us for the duration (but even that won’t help up past some 100 G’s, and I doubt it’ll help even with the intermediate range for more than a short while), or some form of inertial dampener to cancel out the g-forces. I should note that in that time, you would have crossed 57.3 billion kilometers, or 382 AU, ten times the distance to Pluto. Even in the first day you would have crossed 1.22 AU, which would put you close to the asteroid belt, and you’d have done 4.88 AU by the second, which will put you just past Jupiter, which is to say that practically anywhere you want to go in the solar system you could reach within 4 days (you need to spend as much time decelerating, in which time you’ll cross just as much distance again), so acceleration isn’t as big a problem as it seems. Interstellar voyages that might require such speed would take so long (many decades) as to make the acceleration period irrelevant anyhow, so such ships would probably take their sweet time ramping up, putting less strain on their engines.
The answer to the life support question involves a lot of explanation so I decided to post it separately.