Supercavitating 'Em Steered Starship: Riding in Plasma Bubble

Starship’s recent test No. 4 was super exciting and breathtaking.

So, how can we improve its weakest point - the hinge and the gaps around the flaps?

Flaps exposed to essentially a plasma torch on steroids, trying to exploit any material flaw, no matter how small, and level anything uneven in a way?

The first crazy Idea I got was to pump inert Argon gas into the spaces between tiles to prevent or delay forming a plasma layer on top of them by cooling.

Spacecraft typically enter Earth's atmosphere at about 7-8 km/s.

At these speeds, the air in front of the craft can reach temperatures of 10,000K to 20,000K.

Plasma typically starts forming when a significant fraction of the gas becomes ionized. For argon, substantial ionization begins at temperatures around 15,000-20,000 K.

Increasing gas pressure, we pump between tiles in theory raises the temperature at which plasma forms.

We might need pressures 10-100 MPa higher to suppress plasma formation meaningfully. I don't know how feasible that is.

Much more feasible is perhaps not preventing but redirecting where plasma forms.

The Bubble

In theory, we could form an argon gas bubble in which the plasma doesn’t touch the vehicle surface and forms a natural barrier, where the rest of the oxygen and nitrogen second plasma layer forms later.

i.e. similar trick which supercavitating torpedoes used since long time ago to have actual zero surface drag/contact with water and move supersonic even in water.

Argon ?

Argon is a noble gas with low thermal conductivity. A high-pressure layer of neutral argon could act as an effective thermal insulator.

Argon does have a higher ionization energy (15.7 eV) compared to nitrogen (14.5 eV) and oxygen (13.6 eV) thus would form a plasma at a slightly higher temperature than air.

Another motivation for argon were the fascinating results of Ioffe group experiment and also how it is used in DARPA’s old/new X-plane concept CRANE as explained later in this article.

if we can prevent redirect or delay plasma formation long enough in these critical 10 minutes, then in theory, cheap gas compared to ablative tiles doesn’t add weight, complexity, manufacturing, installing, checking delays. It also protects large areas fast, has lesser chance of weak spots as each molecule is nonstop replaced, and has probably better redundancy.

Our Induced plasma layer is also expected to be more stable too, as the gas composition flow and presence is in this case controlled by us.

When less is more

Distribute just from behind special heavy tip tile to simplify and reduce parts.

What if we control 2 axes of gas spraying tip as on that supersonic torpedo. What material the tip should be from?

Can uneven noble gas spray from tip cause bigger drag on one side thus be form of vectoring control?

Once plasma forms. we can use 4 tiny electromagnetic coils at tip to shape that plasma and have literally movable virtual flaps from forcefield. We can shape it to oval which we can rotate etc.

Other Gas Choices

When two different plasmas meet, they don't simply mix like neutral gases. Their interaction is complex and governed by electromagnetic forces.

Argon plasma vs. air plasma:

If argon forms a plasma before the air does, it could create a barrier of charged particles.

This argon plasma layer could potentially interact with and impede the incoming air plasma.

Plasma penetration:

The ability of air plasma to penetrate the argon plasma would depend on several factors: a) Relative density of the plasmas b) Temperature and energy of each plasma c) Magnetic and electric fields generated by the plasmas d) Velocity of the incoming air relative to the argon plasma

Plasma formation timing:

If argon forms a plasma sooner than air (due to being pre-heated by compression or other means), it might have time to establish a more stable shielding layer.

Pure Argon Bubble: Advantages:

Acts as a thermal insulator due to argon's low thermal conductivity

Could provide a buffer zone, delaying the formation of air plasma near the vehicle surface

Simpler to implement and maintain compared to a plasma bubble

Disadvantages:

Less effective at deflecting charged particles from the air plasma

May disperse more quickly in the hypersonic flow

Argon Plasma Bubble: Advantages:

Could interact electromagnetically with the incoming air plasma, potentially deflecting it more effectively

Might absorb more energy through ionization and electromagnetic interactions

Could potentially be shaped or controlled using magnetic fields

Disadvantages:

More complex to create and maintain

Once ionized, loses some of argon's insulating properties

Alternative Gases for Plasma Bubble:

If we're specifically aiming for a plasma bubble, we might consider gases with different properties:

Xenon:

Higher atomic mass could provide a more stable bubble

Lower ionization energy, easier to maintain as plasma

Krypton:

Properties between argon and xenon

Could be a balance between effectiveness and cost

Helium:

Very low molecular weight, which could help with weight savings

High ionization energy might help it maintain non-plasma state longer in outer layers

Nitrogen:

Abundant and cheap

Similar to air, so its plasma characteristics might interact more predictably with air plasma

Considerations for Choice:

Ionization energy: Lower ionization energy makes plasma formation easier to maintain

Atomic mass: Heavier atoms might form a more stable bubble but add more weight

Control without Flaps

As for using gas just for supersonic vectoring and getting rid of flaps with motors batteries and hard to insulate gaps.

DARPA's X-plane concept CRANE eliminated moving external control surfaces, reducing aerodynamic drag, which is critical at hypersonic speeds, and increasing fuel efficiency

Less Drag

The experiment at NASA's Langley Research Center heavily simulated and tested an old idea developed by Russian researchers during the Cold War - that injecting ions into the flow around a high-speed craft can dramatically reduce drag.

DARPA did a lot of simulations

During The Cold War, the Ioffe group conducted an experiment where they propelled a steel sphere, about the size of a marble, at a speed of 1 km/s through a tube filled with low-pressure argon gas.

A section of the gas in the tube was ionized to form a plasma. The team captured footage of the shock wave surrounding the sphere before and after it entered the plasma.

The shock wave seemed to stand twice as far from the sphere as its position in a regular gas, resulting in a substantial 30 percent reduction in drag.

These results seem shocking, considering that aeronautical engineers typically struggle to reduce drag by mere fractions of a percent.

In theory, this could have a huge benefit, potentially lowering drag and heat and offering better longevity and reusability of heat tiles.

Less Weight

If tip gas vectoring works enough (Maybe a two-tube body is more stable yet redundant at the same time). Then just imagine all the weight (50+tonnes?) and complex sources of potential failures that you can now remove with flaps motors batteries tiles from the starship.