New Mars Forums

It sounds like you did the right sorts of things to define a best L/D trajectory.  That would be very nearly a constant dynamic pressure trajectory,  such as was studied decades ago.  Yes,  there's some variation of the angle of attack that gets you best L/D,  as Mach number varies,  but I do understand the concept you are trying to employ. 

Lessee,  Mach 0.3 at sea level would be a dynamic pressure of about 133 lb/sq.ft,  which would be about 6.37 KPa,  unless I missed a key somewhere.  That's rather low.  Is that about what you are trying to fly?  They were looking at 1000 psf+ in the old days!  So too,  are you,  I would think.  Mach 1 at sea level is 1480 psf.  I rather doubt you can come off the sled,  manage to start climbing,  and still quickly accelerate to a real flying speed,  at any sort of optimal L/D.  You must get onto the right trajectory at the right speed any way that you can,  then you can control to best L/D (or to constant dynamic pressure,  as a pretty good approximation). 

My only caveats are (1) do you actually have the thrust to make that best L/D (or constant q) trajectory actually happen,  which was always the bugaboo with it decades ago,  and (2) while CFD is your only available option for estimating hypersonic aerodynamics and heat transfer,  be aware it can still seriously lie to you about what happens inside hypersonic airbreathing engines.  Just having a good turbulence model and heat transfer correlations is not sufficient to model all the processes going on inside all but the simplest propulsion devices. It can become a garbage-in/garbage-out problem pretty quickly. 

L = CL q S for the lift force and L = W*cos(theta) - T*sin(AOA) is the normal-to-path force equilibrium,  where theta is the path angle above horizontal.  That means (W/S)*cos(theta) = CL*q for your trajectory,  ignoring the T*sin(AOA) term,  which should be rather small.  In turn,  if the best CL is near 0.5 in value as a guess,  that says your wing loading is CL*q/cos(theta),  or somewhere in the vicinity of 60-70 psf at fairly low path angles,  which I do not find credible for a re-entry-qualified craft.  Something at or above 100 psf is more credible.

Along the path,  the force equilibrium (for no pathwise or cross-path acceleration) is T*cos(AOA) = D + W*sin(theta),  and you must further exceed that equilibrium thrust T by the amount that will actually accelerate you to the next speed and altitude along your trajectory,  at whatever mass you have at that time point.  It takes something resembling a trajectory code to properly explore that.

Have you done anything to define the thrust requirements all along your trajectory,  using that kind of free body diagram calculation embedded in some proper code?  You should have,  for any realism at all.  Once that is defined,  then you have to figure out what sorts of propulsion items you must have,  that can supply those amounts of thrust,  at all of those speeds and altitudes. 

You will find the airbreathers start to fall well short in the thin air down nearer 30-40 km than up nearer 50 or 60 km.  Their thrust is rather closely proportional to combustion chamber pressure,  which is in turn a fairly fixed ratio to ambient pressure,  for pretty much any type of jet engine imaginable.  Once the air thins too far,  you have no chamber pressure,  because 3 to 6 times essentially nothing is still nothing,  for ramjets and scramjets!  Which means in turn your airbreather thrust is essentially nothing.  And if the thrust force is near nothing,  then the higher airbreather Isp is worthless to you!  Simple as that.

I'm not saying your designs won't work,  because I do not know enough about them to figure anything.  I'm just saying you have to worry about a whole lot more than just L/D and Isp. 

GW

Your time comparisons are apples and oranges. 

Reentry only takes 30 minutes if you time it from the reentry burn instead of the entry interface altitude of 140 km.  From there,  using a low-angle trajectory,  it's about 3 to 4 minutes from entry at orbital speed to a fairly sudden drop from near-orbital speed to well-below orbital speed,  the max-gee "point",  which is several seconds long actually.  The several-second-long max heating "point" precedes this by several seconds.  Then within several seconds more,  you are "out of hypersonics" at about Mach 3 speed,  if you are blunt.  That's 4-5 minutes from interface to out of hypersonics.  It works this way because most of your descent is above half orbital speed,  for a short time exposure to the most extreme entry heating.  The peak gees is usually somewhere around 4 gees. 

The ascent heating exposure is a lot longer than that,  because most of your ascent time is for when you are below half orbital speed,  and very little exposure time above it.  While not as extreme,  simple hypersonic heating is still quite severe. And you will NOT suddenly gain a lot of speed at 4-ish gees,  unlike descent,  because unless you are a rocket,  there is no way your propulsion will support accelerations like that.  The altitude is too high (around 40 km,  near 140,000 feet) and the air too thin (almost a vacuum) for any airbreather to accelerate anything. 

Using a rocket there is a waste of rocket propellant that should have been used instead on the non-lifting ballistic ascent trajectory that leaves the sensible atmosphere at only high-supersonic speeds,  not even hypersonic. 

GW

Take off from a runway search

AI Overview
Determining the precise runway launch length for a hypothetical "space plane" or future runway-launched spacecraft is complex, as it depends heavily on the specific design, weight, and desired flight profile of the vehicle.
However, we can look at existing and proposed spaceplane systems and their runway requirements for landing, which can provide insights into potential launch needs:
Space Shuttle: The Space Shuttle orbiters landed on a 15,000-foot (4,572-meter) concrete runway at the Kennedy Space Center (SLF), according to NASA.gov. While the Shuttle launched vertically, this demonstrates the significant runway length required for landing a vehicle returning from space at high speeds.
Stratolaunch: This aircraft, designed to air-launch rockets carrying spacecraft, requires a 12,000-foot (3,700-meter) runway for takeoff.
Radian One: This proposed spaceplane aims to take off horizontally from a runway and fly directly into orbit. While the exact runway length needed is still under development, a Futurism article suggests it will utilize a rocket-powered sled for initial acceleration.
Virgin Galactic's SpaceShipTwo: This suborbital spaceplane takes off on a 2-mile (approximately 10,500 feet or 3,200 meters) runway, attached to a carrier aircraft, before being released at altitude to proceed under its own power.
In conclusion, while there isn't a universally standardized runway launch length for spaceplanes, based on existing and proposed systems, it's evident that runways in the range of 10,000 to 15,000 feet (approximately 3 to 4.6 kilometers) or longer would be necessary to accommodate future spaceplanes designed for horizontal takeoff, and even longer runways or additional launch assistance might be needed for orbital launches. This is considerably longer than the runways required for typical commercial aircraft, which generally fall within the 1,500 to 3,000 meter range.

I call gasses that do not condense, "Carrier Gasses".  Nitrogen and Argon are in that category on Mars.  On Earth, in addition, both CO2 and O2 are also "Carrier Gasses".  They Carry heat from warm places to colder places while mostly not condensing.  So, yes if you warm Mars enough, then CO2 becomes a "Carrier Gas" on Mars.  If we could release lots of O2 from water to the Mars atmosphere, we could increase the carrier gas, and so in that case the Mars atmosphere becoming thicker, could help to move heat from the warmer places to the colder places, and so help to keep CO2 warm above the condensation point.  A situation I have concern over in such a case, lets say the Mars atmosphere becoming 1/2 what it is now with a matching content of O2, may be the production of large amounts of CO.

But an atmosphere with lots of O2 and CO would be a potential energy source.  But microbes might consume these substances and produce CO2.

The value of greenhouse gasses and particle method heating are that they will warm the cold areas more than they will warm warmer areas.

So, impactor energy would be conserved to a best purpose, if you also used greenhouse gasses and particle method heating.  You may have missed what I indicate by particle method heating.

https://news.uchicago.edu/story/scienti … -warm-mars
Quote:

Scientists lay out revolutionary method to warm Mars
UChicago, Northwestern study suggests new approach to warm Mars could be 5,000 times more efficient than previous proposals

Another way to warm Mars and produce Oxygen to add to the atmosphere would be to expose ice from under dirt, or slam an icy object(s) into the planet, or pump water vapor out of "Smokestacks".
https://www.pnas.org/doi/10.1073/pnas.2101959118
Quote:

Warm early Mars surface enabled by high-altitude water ice clouds
Edwin S. Kite https://orcid.org/0000-0002-1426-1186 kite@uchicago.edu, Liam J. Steele https://orcid.org/0000-0002-6611-0179, Michael A. Mischna https://orcid.org/0000-0002-8022-5319, and Mark I. Richardson https://orcid.org/0000-0001-9633-4141Authors Info & Affiliations
Edited by Mark Thiemens, University of California San Diego, La Jolla, CA, and approved March 10, 2021 (received for review February 4, 2021)
April 26, 2021
118 (18) e2101959118
https://doi.org/10.1073/pnas.2101959118

So, the way to have this favorable condition of high-altitude water clouds, is to have just the right amount of exposed ice or water on the surface of Mars.  Currently it has too little exposed ice/water.

But Mars does have ice fogs on occasion, and so in the nighttime the moisture in the higher atmosphere appears to drop downward.

If you had steam turbines that could work with an inner loop of clean water, that is cooled by evaporating less clean water, you could expel the steam to atmosphere, and I speculate that you could use microwave beams to cause the vapor stream to rise up to the high altitudes.  Further using microwaves might allow the Natural UV so to split the H20 into Oxygen and Hydrogen.  The Hydrogen would drift off, and you would have in increase of the "Carrier Gas" Oxygen.

The import of Nitrogen, perhaps from Comets would be additional useful.

So, a combination of methods would most likely be more productive than just impactors.  At least I speculate that is will turn out to be so.

Ending Pending

OK, we are not getting anywhere are we.

How about this article: https://www.universetoday.com/articles/ … -asteroids  Quote:

Terraforming Mars Will Require Hitting It With Mulitple Asteroids
By Andy Tomaswick - April 7, 2025 at 10:51 AM UTC | Planetary Science

It is actually fairly supportive of your position.  I presume you want a pressurization great enough to get rid of spacesuits on the ground, and open bodies of water.  I get annoyed when they talk about asteroids but then talk about getting things from the Kuiper Belt or Oort Cloud.

Quote:

[However, after some brief calculations, Dr. Czechowski realized it would take 15,000 years to get a reasonably sized Oort Cloud object near enough to Mars to make a material impact on its atmosphere.

Impact is the optimal word as well, as the model these calculations describe slams the small body into Mars itself, thereby releasing both its material and a large enough of energy that helps warm the planet. Kuiper Belt objects seem the best fit for this, as they contain a lot of water and could theoretically be brought to Mars over decades rather than millennia. However, they are also very unpredictable when brought close to the Sun. They could fall apart, with some of the material going to waste in the inner solar system, especially if the technique used to send them into the inner solar system involves a gravity assist. Such a maneuver could tear apart these relatively loosely held-together balls of ice and rock.

Dr. Czechowski's final conclusion is simple - at least in theory, we can get enough material to dramatically increase Mars' atmospheric pressure to a point where it is tolerable for humans - or at least to a point where they don't die immediately when exposed to it. However, doing so will require us to crash a sizeable icy body from the Kuiper Belt into it. To do that, engineers would need to design a propulsion system that doesn't rely on gravity to direct the icy body. In the conclusion of his paper, Dr. Czechowski suggests a fusion reactor powering an ion engine but doesn't provide many details about what that system would look like.

I am not prepared to wait 15,000 year for the Oort Cloud delivery.  Kuiper Belt deliveries look more possible in a shorter time period.

Maybe your nuclear explosion method may have merit, I am not capable of calculating that.

And I wonder if you and I have the same notion of what practical terraforming could be?  I am the intruder so can only offer that I think that if a pressure of 10 millibar over the south pole and maybe 2.5 * 9 millibars over the north pole could be achieved, that could be an initial victory.  Perhaps 23.5 millibars pressure.

The north polar environment could be sportive of some kind of biosphere of significance.  Particularly if plants can be bio formed to be adaptive to that environment.

So, the idea of the "Comets" is to get water and Nitrogen to Mars in large quantities.  Mars already has a considerable amount of water.  While it would be wonderful to get more Nitrogen, it is not a necessity to achieve what I consider an initial terraform goal.

It remains to be seen if an asteroid with an solar elliptical orbit could punch a hole in the crust of Mars, and if that hole would fill with ground or ice water.  The heat from the impact would likely keep hydrothermal water flowing for some time into the lake.  Obviously any hope of keeping it from evaporating relies on a ice cover, and perhaps intervention from humans and their robots to cover it with domes.

But then it would help to start a biosphere perhaps.

And eventually in 50 year or 100 years if you could get a comet from the Kuiper belt maybe you could do your thing.

But objects like Ceres, 10 Hygea, and Callisto may very well contain a lot of Ammonia, which if delivered to Mars could alter things.  It sounds like far too much work, but if you have robots doing the work, then it is simply unfamiliar not impossible.

But I regret offering what I have offered, it only seems to annoy you.  I would prefer to not annoy you and to have not said anything about asteroids.

I apologize and withdraw.

Ending Pending

It is not important.  Should you decide to do an asteroid you could.  If you have the means you might do a comet.

The Dinasaur killer was about 10km or 6 miles in diameter, I believe and many of the asteroids that cross both Earth and Mars orbits are maybe 1.5km or 3km, which is much more manageable A big one would mess up existing human structures on Mars.  Smaller can be better.

And a cratering event could also be used to uncover the overburden over a mineral deposit.

Yes if you have the means, you can do your comets, but why then should you forbid the asteroids?

PhotonBytes,

I have given it some thought, and think at least part of your intentions could be useful.  The specific method to melt one hemisphere, and not the other, could include comet collisions, and perhaps other things.

I recently saw an article about why the North and South Hemispheres are different.  Here are some articles:
https://www.universetoday.com/articles/ … emispheres
https://universemagazine.com/en/differe … al-causes/
Quote:

January 20, 2025
Difference in the hemispheres of Mars is due to internal causes

Oleksandr Burlaka
The Northern and Southern Hemispheres of Mars differ greatly in their topography. The first one is predominantly lowland, while the second one is mountainous. As the researchers found out, the reason for this is magmatic activity inside the planet.

  Image Quote: https://universemagazine.com/wp-content … 36x964.jpg

So, the South Hemisphere, is relatively elevated relative to the North.  The exception is the Hellas Depression.

Basically, since there are two poles, we can take two pathways for Mars.  Melt the North Polar ice cap and make lots of canals and lakes from it.

But keep the south polar ice cap intact and carve a city into it.  The CO2 solids would be desirable to evaporate and keep evaporated.

My vision of how Mars deteriorated over time as per atmospheric pressure and water reserves, includes a time period where the Southern Hemisphere mostly would have already have become more Mars-like but the Northern Hemisphere would remain somewhat like Earth.  In this visualization, the Southern Hemisphere would mostly be in stratospheric conditions, while the Northern Hemisphere would retain a troposphere, and some ability for liquid water rain and melting snow events.

A troposphere would hold some water vapor as a greenhouse gas, and presumably would have significant amounts of CO2, and some Nitrogen and Argon.

https://en.wikipedia.org/wiki/Troposphere
Image Quote: https://upload.wikimedia.org/wikipedia/ … en.svg.png

So, I would say that most of the up-pressure from evaporating the South Polar ice cap will settle into the Northern Hemisphere as a more pressurized gas.

I would argue that first things might be to warm the atmosphere with particles and greenhouse gasses first, and then perhaps to direct some comets and asteroids with intentions to modify the Northern Hemisphere.

And of course I am also a fan of solar power satellites to beam power down, to various places.  But using the Northern Hemisphere of Mars as a collision energy collector is an interesting notion.

I would not be a fan of it, but I suspect that if 10 Hygea or Ceres were modified to be a major settlement effort, they could send methods to modify a comet or asteroids path to such an object to move it's pathway.

There are many Mars crossing asteroids that might also be manipulated: https://en.wikipedia.org/wiki/List_of_M … or_planets
Quote:

List of Mars-crossing minor planets

Some of these may even be a threat to Earth so colliding them with Mars might be of some use to Earth.

Ending Pending

I think we need to break the comets into smaller pieces before sending them into the inner solar system.  Tsar bombs are likely to fragment comets uncontrollably.  And the political issues with building them makes this idea unlikely to succeed.  It would violate the test ban treaty.  The fission rocket idea is possible, but I suspect it would strain the Earth's supply of fissile material if deployed on a large scale.  Fusion-fission hybrid propulsion using a mixture of DU and thorium may be more sustainable.  We use fusion to produce the neutrons needed for fast fission.