Space Carrier VARUHARA notes - Stealth tactics in space
I've redesigned the spacecraft in Space Carrier VARUHARA to emphasize stealth.
The Valhalla is a late war carrier designed for rapid production at the expense of redundant systems and flexibility.STEALTH DESIGN
Valhalla's angular shape assists radar/lidar steatlh.
The short side is the main sunshade; it's mirrored to reflect sunlight into a narrow cone. Most of the time, the ship hides in the shadow of this sunshade.
The long side is also a mirrored sunshade. This allows aiming the catapult when needed.
The other sides are black, to eliminate reflections of moonlight/planetlight.
All sides are cooled by liquid helium or liquid hydrogen. Liquid hydrogen is used in interplanetary space because it has much better heat of vaporization, but liquid helium is used when it's necessary to "bottle up".
The main thrusters are hidden within tunnels, so they are only visible in a narrow cone. They use pulsed operation to increase expansion ratio so the exhaust is cold. The propellants used are:
1) (Molecular) hydrogen - this is the main propellant used, heated by fission reactor. Hydrogen is hard for enemy sensors to detect, but easier than helium. Specific impulse is 850s.
2) helium - this propellant is used when extra stealth is needed. It is also heated by fission reactor. Specific impulse is 600s.
3) LH2/lox - Hydrolox is used in situations where relaxed stealth is practical, because LH2 consumption is halved and LOX is a conveniently dense fuel. In particular, it's used for the main transfer burns at planetary periapsis. The exhaust is normally very visible because ice particles reflect sunlight. But this isn't a problem when thrusting in the night shadow of a planet/moon. Specific impulse is 450s.STEALTH TACTICS
When in orbit in contested space, the ship "bottles up" during most of the orbit. This means cooling the outer surfaces with helium, and melting ice to absorb internally generated heat. If helium supply is low, hydrogen is used instead - although this makes the ship warm enough to see with helium cooled sensors.
At periapsis, the ship refreezes the ice with liquid hydrogen. This hydrogen will be difficult to see against the background of the much warmer planet.
At all times, the boiled off helium and hydrogen will be run through the reactor before being expelled out of a main thruster. You might as well get some maneuvering thrust out of it, to hopefully throw off enemy predictive tracking. Even when the reactor is shut off, the core will remain hot.
Even though most military spacecraft have similar stealth abilities, a completely unseen approach is rare. The occasional detection by sunlight beam or star occultation is enough to provide a rough idea of where enemies are located - but this data isn't frequent or precise enough to provide a firing solution. Pre-war theory was "there is no stealth in space", meaning that an approaching attacker will always be detected and always be tracked well enough for lasers to prevail. Long range stealth missiles destroyed many laser battleships until crews changed tactics to emphasize stealth. New warship builds tended to be missile bus carriers to save costs compared to laser battleships and to reduce minimum reactor waste heat generation.
The perception is that laser battleships were made obsolete by missile bus carriers, but in fact the case is not so clear cut. At the time of the war, stealth had an edge over sensors. But if sensors regain the edge, then high power beam weapons could regain the advantage.SENSORS
Valhalla's main sensors are:
Helium cooled thermal telescopes. These can see anything that isn't itself helium cooled, although not against a planet/moon.
Optical cameras - occultation sensing. These stare at the background stars and detect the dimming or distinctive diffraction pattern of a passing object. This can see anything, but at limited range and can't track.
Optical cameras - sunlight/thruster sensing. The cameras may also get lucky seeing reflected sunlight or a thruster. In this case, the detection may last long enough to get a rough heading.
Scanning Electron Beam/Telescope. Shine an electron beam onto a target; observe with a telescope. This can see anything at short range, including against a planet background. Electron beam telescope is particularly useful for stealth spacecraft because they are deflected by ambient magnetic fields. As such, the target has a much less precise idea of where the beam is coming from. In contrast, radar and lidar give the target a precise angular location and thus a precise direction to point tracking sensors back.
Neutron beam. The neutron beam is a weapon, but it can also be used to find out stuff about enemy targets. In particular, they can be used to distinguish decoys and detect nuclear warheads and materials.
Valhalla lacks radar, depending entirely on fighters/drones for radar sensing. Most military spacecraft have radar stealth, so this limitation is accepted.WEAPONS
Valhalla's main weapons are:
Valhund fighters. Valhalla can catapult a Valhund up to 250m/s in 5s; it can slow down incoming fighters with a volley of reusable bullets. Each Valhund is armed with a hydrogen/hydrolox gas gun that launches small triple missile burgers. Hydrogen is used for low muzzle velocity; hydrolox is used for high muzzle velocity at the expense of stealth. Each missle burger can immediately split up into three short range missiles, or it can act as a single two stage missile. The "buns" act as the first stage, but retain a small amount of fuel so they can act as orbital "space mines". The "meat" acts as the second stage.
Hydrogen gas gun. Valhalla has a gas gun which can shoot reusable bullets at an extremely high rate. It's optimized for use in fighter braking, and mounted near the reactor. However, it can be used as a short range weapon.
Neutron beam. Neutron beams were developed just before the war, using plasma wakefield acceleration within a solenoid magnetic field. The solenoid means that the ambient electrons rushing into the plasma wake "miss" the exact center of the beamline and form a strong magnetic field at the beamline. This moving magnetic field accelerates the neutrons (which have a magnetic moment). Neutron beams are not very efficient, so few countries anticipated their importance in the war. But they would be able to disable nuclear warheads and cause most guidance electronics to fail.
Valhalla lacks electron beam armament. The neutron beam is powered by an electron accelerator parallel to the catapult, but this electron beam has too much self repulsion to be a practical weapon. It does, however, use the electron beam in a low power mode for the scanning electron beam telescope.
Valhalla lacks laser armament. Pre-war warships typically had heavy laser armament, but this required them to use large hot radiators and/or large solar arrays. Either way, they were highly visible and the advances in stealth missiles made them too vulnerable. Late war warships would typically have much smaller reactors insufficiently powerful for heavy lasers.
Valhalla lacks missile launchers; it depends entirely on its fighter wing to launch missiles.DEFENSE
Obviously, the main defense is stealth - avoid detection, and try and throw off tracking. But there's also Whipple shielding - 3 layers of metal sheet to defend against random space debris and small bullets/fragments. Additionally, burger missiles are used to shoot incoming missiles (Valhalla lacks missile launchers, but at least one Valhund should normally be nearby defending the ship.) The neutron beam has limited effectiveness against late war missiles, but the ability to neutralize nuclear warheads alone justifies its continued use. The gas gun is not really an effective weapon, with a low muzzle velocity and light unguided bullets. But it's better than nothing as a last ditch defense.LOGISTICS
Apparently this isn't obvious to everyone, but it's actually really easy to dock and receive supplies from supply ships in space. Here on Earth's ocean, ships can't just dock with each other due to the way the ocean moves. But in space, there's no ocean. So, Valhalla was not designed to carry a bunch of long term supplies on board. Stealth supply drone ships are bigger, and are shaped like square base obelisks. Despite being larger, supply drones are less expensive than warships.
Even less expensive are civilian supply ships and stations. Usually Valhalla breaks stealth to directly receive supplies from civilian ships, relying upon stealthy hydrogen propulsion later on to throw off tracking. It's also possible to tug cargo containers and tanks with a Valhund fighter, using a large sun shield for some semblance of stealth carrying the containers/tanks to/from Valhalla. However, this is more time consuming and costly, so Valhalla doesn't bother. It's currently patrolling in the Jupiter system, where hydrogen fuel supplies are not so available (most spacecraft only pass through the Jupiter system for its gravity boost). So its operations heavily emphasize conserving hydrogen.
Valhalla's current patrol orbit passes by Callisto, given the crew a view of its namesake crater about twice a month. Before the war, Callisto had LH2 refineries, but these were destroyed in the war. Most of Callisto's current industry revolves around cheaper and more storable methane fuel, along with lox, water, and carbon dioxide. These supply civilian stations just fine, but neither Valhalla nor its Valhund space fighters can use methane fuel. In contrast, its Dauber scouts use pre-war modular booster packs. Methane-lox boosters aren't very stealthy, with water and CO2 ice particles in the exhaust. So, Dauber scouts from Valhalla try to only make mid-course return thrust maneuvers in the shadow of Jupiter or Callisto. (The initial catapult boost and gas gun braking are stealthy enough, but a mid-course maneuver is usually required to return back to the carrier.)