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I just found out that @Winchell Chung (Atomic Rockets) is in the hospital with a terminal prognosis. I can't say what I'm feeling, so I'm just passing it along for those who don't already know.

#SF #ScienceFiction #OGRE #Space #SpaceTechnology
 
An ISRU first - refining O2 and CO on Mars.

https://mars.nasa.gov/news/8926/nasas-perseverance-mars-rover-extracts-first-oxygen-from-red-planet/

Obviously, generating oxygen is very useful. Less obvious is that carbon monoxide can be a useful fuel. The specific impulse of a CO-LOX rocket could be over 300s, and realistically a specific impulse of 290s may be reasonable. This is good enough for an SSTO from Mars. It's also good enough for interplanetary missions from Mars.

Carbon dioxide could be harvested without landing on Mars or Venus, via orbital atmospheric scooping. This would allow mining satellites to generate fuel without dealing with various losses and operational difficulties of landing and launching.

#Space #SpaceExploration #SpaceTechnology
 
Okay, so I've decided to actually work on a Space Carrier VARUHARA board game system, even if only to help me study tactics and strategy for the story.

I'm adapting my ideas to line drawing, because that lets me keep a record I can refer to and refine.

That means drawing lines on millimeter graph paper; each map consists of multiple 8.5x11 sheets (with margins, since printers don't print edge-to-edge). So each sheet is just 20x25cm.

Scale is designed for Earth out to GEO, or a bit more than 80,000km across. At a scale of 1cm:1000km, that's about 80x80, or 5x5 sheets (100,000km x 125,000km).

SCALE = 1cm to 1000km

SHEET = 20cm x 25cm

MAP = 5x5 sheets (100,000km x 125,000km); without corners this is 21 sheets

Earth is the center sheet, consuming about 64% of the width. The area within Earth's circle is optionally used for orbit inclination tracking, for true 3D movement.

Earth is surrounded by rings indicating gravity strength.

The use of millimeter graph paper enables really good precision - down to a fraction of a millimeter, or less than 100km.

An intercept is registered if two line segments cross (and optional inclination indicates close enough Z match). This is a bit of a fudge, but I think it's close enough for my purposes.

However, to achieve greater precision I use a "Tangent Vector Movement System". A ship's position is implicitly defined by a tangent between a PAST dot and a FUTURE dot. The line segment between these dots is tangent to the ship's true position and path.

The way it works is that time is broken into "measures", and the dots are projections of the ship's tangent into the PAST and FUTURE times, on measure breaks. Each measure is broken down into four quarters.

MEASURE = 4000 seconds (about 1 hour)
QUARTER = 1000 seconds (about 17 minutes)

Using this tangent system makes it easier to visualize future positions, and reduces how much work is needed because units orbit without thrusting most of the time.

The actual position of a ship is implicitly designated by a point along this tangent. For example, on quarter 2, the ship is at the midpoint of the tangent. But you don't actually draw this point if you don't want to.

More thoughts later ...

#gizmo #worldbuilding #SpaceCombat #SpaceTechnology #SpaceCarrierValhalla
 
Image/Photo

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.)

#gizmo #worldbuilding #SpaceCombat #SpaceTechnology #SpaceCarrierValhalla
 

Scanning Electron Telescopes vs Hard UV Lidar vs RADAR


So, I'm working on my Space Carrier VARUHARA setting, and have decided the ships and fighters and such will use stealth after all.

The Valhalla looks like a trapezoid slab, with a mirror sun shield on the shortest side and the catapult along the longest side. This side is also mirrored. The other four sides are black to absorb light from a nearby planet/moon.

The main thrusters use helium propellant when operating in contested space, which is really hard to see, but also hydrogen at periapsis where the planet/moon makes it hard to see.

Nevertheless, it's possible to sporadically detect the Valhalla when a sensor is in its reflected sunlight beam, or due to occultations.

But sporadic detections aren't good enough to directly hit a target with weapons.

What could they use for tracking? Here are a few candidates I've thought of:

1) Radar Radar stealth is good, but is it ever going to be perfect? Maybe just amp up the power enough, and radar's still the best option?

2) Hard UV Lidar Mirrors might defeat optical lidar, but hard UV or soft X-rays will produce backscatter no matter what. Is this a better option than radar?

3) Scanning Electron beam I'm not sure precisely how this would work, but basically the idea is to shine an electron beam at the target, and use telescopes to detect photons produced when it hits. Even if self repulsion might make an electron beam unsuitable for use as a high power weapon, it may be good enough to use in a sensor system?

Any ideas how these would compare? Any other good ideas?

Thanks!

#SpaceWarfare #SpaceTechnology #SpaceCombat #gizmo #Space #Astronomy
 

Stealth in Space - Helium propellant instead of LH2 propellant?


Hey, question for @Luke Campbell or @Rhysy or anyone who knows astronomy and stuff ... how visible would cold helium or cold molecular hydrogen exhaust be?

I know interstellar molecular hydrogen is notoriously difficult to detect; would that apply to hydrogen lit by sunlight from 1AU away? I'm guessing helium would be practically impossible to detect. Is that right? Or is it actually easier to detect due to its spectral lines?

Assume we're in interplanetary space vaguely near Earth. Would the exhaust get warmed up by sunlight, or scatter sunlight enough to be visible? I figure hydrolox exhaust would be visible due to the ice particles reflecting/refracting sunlight.

The stealth missile has a helium cooled mirror sunshade to reflect sunlight away in a narrow cone. There's also a side port to receive a laser which warms a heating element. The hot element does radiate light back toward the power laser, but it's unlikely enemy sensors will be lined up with that. OTOH, the laser path might be visible thanks to zodiacal dust? (I'm not sure.)

Anyway, small pulses of helium go through the helium element to produce thrust with a large expansion ratio. I think helium exhaust will be cool without an excessively bulky thruster, whereas that may be difficult with hydrogen due to the multi-atomic molecule. Specific impulse is perhaps 600s, which is more than enough for interplanetary missions.

Of course, liquid helium is going to be a lot more expensive than liquid hydrogen, and logistically challenging due to the increased boiloff. Liquid helium doesn't have much heat of vaporization, and of course its boiling temperature is colder.

If helium exhaust is practically invisible, then there may be no defense against these stealth missiles other than foiling enemy detection and/or tracking.

#SpaceWarfare #SpaceTechnology #SpaceCombat #gizmo #Space #Astronomy
 
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Solid Rocket Space Missile Guidance Reconsidered ...


Most current space missiles use four liquid/gas divert thrusters arranged up/down/left/right.

But the old ASM-135 ASAT used a bunch of solid rocket thrusters with nozzles arranged around its waist.

https://airandspace.si.edu/sites/default/files/images/collection-objects/record-images/T20140036000cp01.jpg

You can see that the 64 solid rocket tubes are actually parallel to the body, but their nozzles are pointed outward sideways from the center of each tube. 56 of the thrusters are high thrust, while 8 of them are lower thrust for more fine adjustments. The entire MHV rotates at 30 revolutions per second, so continued thrust in a single direction is possible.

The Strix anti-tank mortar round uses a similar divert thruster system, with 12 solid rocket waist thrusters.

Well, for future space combat missiles, why not return to this style of solid rocket guidance? Compared to liquid/gas thrusters, I think solid rocket units could have better acceleration, and the delta-v is not necessarily much worse when you consider the 45 degree penalty of thrusting "between" the four cardinal directions.

Instead of a single layer of somewhat flattened nozzles, I imagine two staggered layers of bell nozzles, one slightly angled forward and the other slightly angled rearward so they all point through the center of mass. And each solid rocket chamber could be partitioned into 4 charge pulses. That way, you could have 64 efficiently large nozzles and 256 charges - some bigger and some smaller.

Compared to a liquid/gas thruster system, this is perhaps cheaper to mass produce and less maintenance. It might also be more compact. But I think the really interesting advantage is that it could be used for a gun launched projectile rather than boosted by a rocket. The projectile might have a stealthy flat face. Note that a gun would typically need to lead the target by a lot in space, so this face will not reflect radar/lidar beams directly back to the target. The face might be pointed, say, 30 degrees away from the target.

This could be an extreme challenge to defend against. It might be impossible to target an incoming guided projectile until it lights up a divert thruster. You might be compelled to perform an occasional evasive maneuver simply to force incoming projectiles to divert.

For guidance, a rear facing receiver could be used for command guidance and/or receive navigation beam data. For example, a beam spiral scanning around the target could implicitly guide multiple projectiles by informing of their relative location compared to the target.

More thoughts on implications for space combat maneuvering and engine/weapon layout to come...

#SpaceWarfare #SpaceTechnology #SpaceCombat #gizmo #Space
 
I'm trying to figure out what are all the basic real life space missile designs so far.

AFAIK, the main design is used by SM-3, THAAD, EKV, etc ... a fixed forward facing sensor and four waist divert thrusters (up/down/left/right). This seems to be the most common design, and it's pretty intuitive. The kill vehicle doesn't rotate, it just stares forward and uses divert thrusters to try and zero out any angular velocity of the target image across the sensor. This is similar to the
"windscreen" principle. If you're flying an aircraft and the enemy is shooting AAA, any tracers that look like a dot on the windscreen are ones headed toward you.

Then there's the Israeli Arrow-3. I'm not 100% clear on what type of rocket thruster is used, but it's fixed to the body. The sensor can point sideways. So, it can't instantly divert in any direction. It must "turn and burn". But a single main thruster weighs less than four thrusters, and it can maneuver "diagonally" more efficiently. Also, it's okay for the center of mass to shift as fuel is consumed.

The ASM-135 ASAT used clusters of single shot thrusters around the cylindrical body, similar to the Dragon missile. I think this style of missile guidance has not endured the test of time. Like the Dragon, it revolved so it would be possible to repeatedly thrust in one direction even though the thruster units are distributed all around.

I don't know if there are any others. There are a number of ASAT and exoatmospheric ABM missiles I know nothing about.

Oh, there's also Deep Impact's Impactor. I think it had one main thruster, pointed sideways, and a few small maneuvering thrusters. I'm not sure whether it used "turn and burn" or if it just rotated and timed its main thruster thrusts according to when it was rotated in the desired direction.

Anyone know?

Thanks!

#Space #SpaceTechnology
 

Ebrahimi's Magnetic Reconnection Plasmoid thruster


I don't know the name of this thruster concept, but it uses magnetic
reconnection to accelerate plasmoids:

https://phys.org/news/2021-01-concept-rocket-thruster-exploits-mechanism.html

This thruster concept stems from her fusion research.

The only performance numbers in this article is a claim that the exhaust
velocities could reach hundreds of kilometers per second. In practical
solar system missions, though, the 40km/s flown in GOCE is near the
sweet spot of keeping propellant mass low while keeping thrust
adequate. So, it's entirely unclear to me whether this thruster offers
compelling advantages.

I'm reminded, of course, by VASIMR, another plasma thruster inspired
by fusion research. It hasn't really gotten far. We still don't know whether
or not it would actually work ... it's unclear whether the plasma exhaust
will cleanly separate from the magnetic field lines, or whether the particles
will loop back around and nullify too much of the thrust.

Still, it sounds like this new concept works with the way plasma interacts
with magnetic fields in real life rather than "fighting" it.

#Space #SpaceExploration #SpaceTechnology #Plasma
 
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