Discussion The next 100 years..

[HopDavid]

SSTO is more of a practicality issue than anything else.

Glancing at your SSTO thread, I see you underestimate problems of SSTO. I left a critique at that thread.

---------- Post added at 09:06 PM ---------- Previous post was at 07:37 PM ----------

Two totally different projects, cannot be directly comapred.

It is you who cited the I.S.S. to argue a sustained Mars presence doesn't need trade and ROI. I quote:

You insist that a permanent presence would require "trade and ROI". Yet the ISS hosts a permanent human presence and doesn't do either of those things.

If you say they ISS and a Mars base can't be compared, then your argument is worthless.

If you are citing I.S.S. as showing a permanent Mars base is doable even without trade and return on investment, it is fair to cite numbers comparing ISS and a Mars base.

Also, who said we need to use Mars Semi-Direct to get to Mars?

If you want to argue a different Mars architecture, produce some numbers. I will look at them. First off I'd like mass to LEO each launch window. Clarke's architecture calls for launching 1.5 ISS. masses each launch window.

And please stop with the "2.14 years" thing.

If we're talking about doing this within NASA's budget, delivery rate is relevant.

The 450 tonne I.S.S. was built over 12+ years. In Clarke's architecture, 619 tonnes would be lofted each 2.14 years. One rate is 36 tonnes per year, the other 324 tonnes per year.

Oh yes! Magical radiation! Radiation will kill your crew, you can't get away from it! Just dead, therefore interplanetary travel is impossible. :facepalm:

If only facepalming and exclamation points could make radiation concerns go away.

Also I said radiation shielding adds to expense and difficulty. I did NOT say makes it impossible. Please stop misrepresenting what I say.

Also, there are workarounds. Look at electromagnetic radiation shielding, for example.

They involve room temperature super conductors? What mass and power requirements? If you can offer cites or numbers, I will learn something. If not, you are wasting my time.

Wait, I thought dV to orbit was some 10 km/s. When did it change to 14 km/s?

Some context has been lost. I will quote upthread:

From earth's surface to LEO is about 9 to 10 km/s. Most BLEO destinations are 13 to 14 km/s or more.

Here is the rocket equation:
(propellant mass + dry mass) / (dry mass) = e^dV/Vexhaust

Hydrogen and oxygen have an exhaust velocity of 4.4 km/s. 3/4.4 is about ln(2). So each 3 km/s added to your delta V budget doubles lift off mass.

Bolded the relevant part for your benefit.

Something about that guy's analysis does not seem right to me...

I'm sorry, "doesn't seem right" without any math arguments fails utterly.

Lox/Hydrogen lower stages have a poor T/W ratio which means big gravity loss. I mentioned this on your hydrogen rocket SSTO thread.

 

[T.Neo]

Glancing at your SSTO thread, I see you underestimate problems of SSTO. I left a critique at that thread.

I don't underestimate the problems of SSTO at all.

Which is why the Orbital Propellant Tanker isn't an SSTO. :tiphat:

If you are citing I.S.S. as showing a permanent Mars base is doable even without trade and return on investment, it is fair to cite numbers comparing ISS and a Mars base.

So because something can be compared from a philosophical or decision-making standpoint, it can also be directly compared from a technological standpoint as well?

:facepalm:

If you want to argue a different Mars architecture, produce some numbers. I will look at them. First off I'd like mass to LEO each launch window. Clarke's architecture calls for launching 1.5 ISS. masses each launch window.

Clarke? Do you mean Arthur C. Clarke?

If we're talking about doing this within NASA's budget, delivery rate is relevant.

The 450 tonne I.S.S. was built over 12+ years. In Clarke's architecture, 619 tonnes would be lofted each 2.14 years. One rate is 36 tonnes per year, the other 324 tonnes per year.

ISS was built by the Shuttle, which had a low flight rate and multiple delays.

As much as Mike Griffin would like to believe, you are not going to assemble a Mars mission using the space shuttle. You would use a more reliable vehicle.

Also, over a hundred tons of mass are already lifted into space each year. The actual combined payload mass is a good deal lower than the 'theoretical' launched mass, but this is because most payloads in our era are launched to GTO or similar orbits. The capability of several hundred tons per year is not mythical.

If only facepalming and exclamation points could make radiation concerns go away.

Also I said radiation shielding adds to expense and difficulty. I did NOT say makes it impossible. Please stop misrepresenting what I say.

The general feeling I get from you is that you believe that certain things are so expensive and difficult to effectively make them impossible.

For example, your comment about facepalming and exclamation points making radiation go away, almost sounds like a statement that any attempt to meaningfully mitigate radiation is wild dreaming or nonsense.

They involve room temperature super conductors? What mass and power requirements? If you can offer cites or numbers, I will learn something. If not, you are wasting my time.

Room temperature superconductors? Where did those, all of a sudden, become a requirement? :dry:

If you want to find out info about electromagnetic shielding against radiation in space, search for it. Here is an interesting document on the matter.

Bolded the relevant part for your benefit.

A single vehicle does not have to deal with that whole 14 km/s requirement.

I'm sorry, "doesn't seem right" without any math arguments fails utterly.

It is not a math argument, it is a plain facts argument. He seems to complain about the engines having to throttle down to alleviate aerodynamic forces... but the Atlas V Heavy, I believe, has to throttle down as well.

He also completely misunderstands the system in place with an inline shuttle derived launch vehicle; the solids are the first stage (stage 0) and they provide most of the thrust. The core stage is effectively just a ground-lit second stage.

In any case, the RS-68A boosts the payload of the D-IVH to ~25 tons, and if I read correctly the D-IVH has a lower liftoff mass than the Atlas V. But is also bulkier, of course, due to the low density of LH2.

 

[Urwumpe]

Having to throttle down for reducing aerodynamic forces and drag losses is not bad. It just means that the engines have to be more complex. But generally, this is a less big problem as it seems. Even if an engine can't throttle to any percentage between 0 and 100%, you often have the case that some useful stable power levels exist that permit the same task with minimal testing. For example only switching between 50% and 100%.

 

[HopDavid]

I don't underestimate the problems of SSTO at all.

Which is why the Orbital Propellant Tanker isn't an SSTO. :tiphat:

Which is why your titled your PDF "Single-Stage-To-Orbit non-reusable propellant tanker".

So, according to you, SSTO isn't Single-Stage-To-Orbit.

So because something can be compared from a philosophical or decision-making standpoint, it can also be directly compared from a technological standpoint as well?

Comparison without numbers and physics is B.S.

Clarke? Do you mean Arthur C. Clarke?

Nope. Obviously you don't bother to read the pdfs I cite.

Also, over a hundred tons of mass are already lifted into space each year. The actual combined payload mass is a good deal lower than the 'theoretical' launched mass, but this is because most payloads in our era are launched to GTO or similar orbits. The capability of several hundred tons per year is not mythical.

300 tonnes to LEO per year may not be mythical, but it won't be cheap.

Also the payloads will need research, the Mars Transfer Vehicles, the cargo vehicles with power sources and plants for ISRU propellant, EDL for massive payloads, all these will take research which boosts expense.

The general feeling I get from you is that you believe that certain things are so expensive and difficult to effectively make them impossible.

Not impossible but less than even odds. Given a 7 billion a year NASA manned space flight budget, I'd place 100 to 1 odds against NASA pulling off a permanent Mars base.

For example, your comment about facepalming and exclamation points making radiation go away, almost sounds like a statement that any attempt to meaningfully mitigate radiation is wild dreaming or nonsense.

What I regard as nonsense is that GCR is a non issue.

It is one of several factors that make the 8 month trip to Mars more difficult and expensive.

If you want to find out info about electromagnetic shielding against radiation in space, search for it. Here is an interesting document on the matter.

Starting at page 41 they start talking about electromagnetic shielding. They do not give these ideas glowing reviews. About the best among the bunch was the plasma inflated field. Which they described as worthy of further research but not showing clear promise. They also say radiation above earth's magnetic field is a genuine concern.

A single vehicle does not have to deal with that whole 14 km/s requirement.

Achieving 14 km/s would probably take a multi-stage expendable.

It is not a math argument, it is a plain facts argument. He seems to complain about the engines having to throttle down to alleviate aerodynamic forces... but the Atlas V Heavy, I believe, has to throttle down as well.

With better ISP comes poor T/W ratio. Bad T/W ratio means lots of of gravity loss. This is a math argument.

---------- Post added at 05:49 AM ---------- Previous post was at 03:48 AM ----------

Having to throttle down for reducing aerodynamic forces and drag losses is not bad.

I was talking about gravity losses, not aerodynamic losses. Do you know the connection between T/W ratio and gravity loss?

But since you mention it, TNeo's 3363 cubic meters of hydrogen would probably incur losses from atmospheric drag as well.

 

[T.Neo]

So, according to you, SSTO isn't Single-Stage-To-Orbit.

According to me, Orbital Propellant Tanker is no longer SSTO.

Comparison without numbers and physics is B.S.

So because you will not trust my assertion that a MTV and the ISS are different spacecraft built for different uses, you insist that they must be directly comparable?

Nope. Obviously you don't bother to read the pdfs I cite.

I do, I just glance over the names of the people who wrote them, sorry.

300 tonnes to LEO per year may not be mythical, but it won't be cheap.

Have you ever added up the LEO payloads of all vehicles launched in a year?

It comes to about 450 tons for 'medium' (Proton or Ariane class) vehicles in a year.

Costs go down as launch rate increases.

Also the payloads will need research, the Mars Transfer Vehicles, the cargo vehicles with power sources and plants for ISRU propellant, EDL for massive payloads, all these will take research which boosts expense.

Yes, of course they will need R&D. And that R&D will be expensive. That R&D will be amortised over each flight?

When did I say otherwise?

Not impossible but less than even odds. Given a 7 billion a year NASA manned space flight budget, I'd place 100 to 1 odds against NASA pulling off a permanent Mars base.

I really do wonder how you made up those statistics. :hmm:

It is one of several factors that make the 8 month trip to Mars more difficult and expensive.

Who said the trip to Mars has to be 8 months long?

Starting at page 41 they start talking about electromagnetic shielding. They do not give these ideas glowing reviews. About the best among the bunch was the plasma inflated field. Which they described as worthy of further research but not showing clear promise. They also say radiation above earth's magnetic field is a genuine concern.

Yes, I am sure they say it is a genuine concern: they are not idiots.

Also, I am not sure what the difference between them giving a "glowing review" to something is in that PDF, and from what you read in that PDF.

Like I said, search for the information. But maybe that is bad advice, because you will purposely seek out "unglowing reviews" of such technology, because you demand it to be impractical.

Achieving 14 km/s would probably take a multi-stage expendable.

Multi stage does not necessitate expendable.

Because it's multi-stage, the individual stages do not have to provide 14 km/s of dV themselves. That's what makes staging attractive.

With better ISP comes poor T/W ratio. Bad T/W ratio means lots of of gravity loss. This is a math argument.

The Saturn V used high T/W RP-1 fueled engines yet crawled away from the launch pad. High ISP is not intrinsically linked with high gravity losses.

Do you know the connection between T/W ratio and gravity loss?

I have my suspicions that Urwumpe does in fact know about the connection between thrust, acceleration, and gravity losses...

But since you mention it, TNeo's 3363 cubic meters of hydrogen would probably incur losses from atmospheric drag as well.

It does not matter whether it is 3363 cubic meters, or 3340 cubic meters, or 3400 cubic meters. There is no need to be repetitively precise.

Drag is not a problem, just as it is not a problem on other launch vehicles. There are multiple vehicle concepts that are purposely quite short and wide (presumably to help mass ratio- less tank surface area for volume), and OPT is relatively slender compared to those.

 

[Urwumpe]

I was talking about gravity losses, not aerodynamic losses. Do you know the connection between T/W ratio and gravity loss?

You are maybe aware that gravity losses are just one factor out of many in the equation and that a good low gravity loss is pretty useless if you ignored the other factors and in the end used more fuel for them.

And yes, I know that amateurs see a connection between T/W ratio and gravity loss and completely ignore the fact that the connection is in reality about flight path angle, altitude (radius) and time. T/W is just one indirectly influencing factor there, not the whole story at all. A good T/W helps, but when optimizing for low gravity losses result in your structure being 5% heavier than a structure that throttles down to keep dynamic pressure low after a strong initial acceleration, you have objectively lost (a lot of) performance.

PS: Even if you could build your rocket out of infinite infinitesimal small rocket stages, you would have limits to the DV that you can get from your rocket. The approximate solution for the infinite stages thought experiment is:

[math]\lambda = e^{-\frac{\Delta v}{\left (1-\sigma \right )w}}[/math]
With [math]\lambda[/math] being the fraction of the payload mass on your lift-off mass. [math]\sigma[/math] is construction mass ratio (stages + engines without payload compared to total mass). w is specific impulse

 

[HopDavid]

So because you will not trust my assertion that a MTV and the ISS are different spacecraft built for different uses, you insist that they must be directly comparable?

It is you comparing I.S.S. to a Mars base.

When I mentioned a permanent human presence on Mars is not sustainable without trade or return on investment, you cited ISS as a counter example.

This is like saying since I can permanently maintain a dog without ROI, I can do the same for an elephant.

When you asked me to demonstrate why the elephant is more expensive than the dog, I mentioned a few numbers. Launch windows, trip times, delta V, etc.

You seem to think numbers are irrelevant, that a Mars base can be made cheap as the ISS through vigorous handwaving.

 

[T.Neo]

It is you who handwaves constantly that a Mars base will be inexorably more costly than the ISS. You don't try to find numbers, you just say "you have to expend so many km/s of dV here, therefore I say it won't work".

Then you continuously compare a philosophical or political aspect of the ISS to its technical nature, which is an absolutely pointless comparison.

You don't even try to find out what the real cost drivers are, or how to reduce or eliminate them. I'm afraid, things like "launch windows, trip times and delta V" are not direct drivers of cost. So please do not repeat those things over and over again.

 

[Sorpenderin]

here is my idea,even though it will probebly never happen

.2014-iss stoped
.2017- ESAs ctv sent
2017 nasa plans signal project
2019 modifyed shuttle goes to L5
2021 iss comes down
2025 private company sends up ETs to create space station
2029 nasa gives signal project to private corperations
2032 ESA sends moon base
2035 first spaceplane
2037 signal project finished
2040 asteroid deflected
2045 chinese moonbase
2052 mars mission
2055 mining of jupiter
2060 alpha centuari probe
2071 nuclear war 2080 earth dead 2100 probe discovers life 2111consitering manned interstealer mission

 

[mojoey]

Someone! Quick! Resurrect James Doohan!!!

 

[Pipcard]

All space agencies will merge to become Starfleet. I mean, you already got some similar logos. (whether they were intentional or not, we don't know)

 

[Codz]

here is my idea,even though it will probebly never happen

.2014-iss stoped
.2017- ESAs ctv sent
2017 nasa plans signal project
2019 modifyed shuttle goes to L5
2021 iss comes down
2025 private company sends up ETs to create space station
2029 nasa gives signal project to private corperations
2032 ESA sends moon base
2035 first spaceplane
2037 signal project finished
2040 asteroid deflected
2045 chinese moonbase
2052 mars mission
2055 mining of jupiter
2060 alpha centuari probe
2071 nuclear war 2080 earth dead 2100 probe discovers life 2111consitering manned interstealer mission

The Space Shuttle was a space plane...

 

[Pipcard]

The Space Shuttle was a space plane...

http://tvtropes.org/pmwiki/pmwiki.php/Main/SpacePlanehttp://tvtropes.org/pmwiki/pmwiki.php/Main/SpacePlane

"In essence, a spaceship that can take off and land like an aircraft, as well as looking like an aircraft." [e.g. Delta Glider]

"The spaceplane must be single-stage-to-orbit or sub-orbit to qualify. Nobody's built one, as of June 2011."

although [ame="http://en.wikipedia.org/wiki/Spaceplane"]that other wiki[/ame] has a slightly different definition that allows the Space Shuttle

 

[Izack]

All space agencies will merge to become Starfleet. I mean, you already got some similar logos. (whether they were intentional or not, we don't know)

That's wild. :blink:

But now I feel left out. :lol:

 

[Codz]

http://tvtropes.org/pmwiki/pmwiki.php/Main/SpacePlanehttp://tvtropes.org/pmwiki/pmwiki.php/Main/SpacePlane

"In essence, a spaceship that can take off and land like an aircraft, as well as looking like an aircraft." [e.g. Delta Glider]

"The spaceplane must be single-stage-to-orbit or sub-orbit to qualify. Nobody's built one, as of June 2011."

although that other wiki has a slightly different definition that allows the Space Shuttle

NASA has repeatedly reffered to the space shuttle as a space plane, and it uses wings to generate lift, as well as a runway to land. It doesn't have to be an SSTO to qualify as a space plane. I'd hardly trust TV Tropes for accurate aerospace definitions.

 

[FADEC]

NASA has repeatedly reffered to the space shuttle as a space plane, and it uses wings to generate lift, as well as a runway to land. It doesn't have to be an SSTO to qualify as a space plane. I'd hardly trust TV Tropes for accurate aerospace definitions.

And the Space Shuttle had the potential capability to take off from a runway on its own: just modify it, i.e. mount engines at the tail instead of OMS pods, just like they did with Buran...

But anyway, the Shuttle flew like a plane. Same principle just without thrust during atmospheric flight. And it was designed to fly into space. So I think it was a space plane very obviously.

 

[T.Neo]

I'd hardly trust TV Tropes for accurate aerospace definitions.

Still, you can hardly criticise the TvTropes definition, since it describes what it describes pretty well- "a spaceship that can take off and land like an aircraft, as well as looking like an aircraft. Many ships have Vertical Take Off Or Landing capabilities, these babies though can use a regular runway too", which is something (i.e. a trope)that appears fairly often in fiction, and something that fits under the broader real-world definition of a spaceplane, even if it isn't a very good definition of spaceplanes as an actual engineering concept.

I think various space agency logos are actually copycats of the NASA meatball (with the red chevron thingy), rather than StarFleet. :lol:

 

[Urwumpe]

But now I feel left out. :lol:

Why? You add the star in the center of the logo. :lol:

 

[TMac3000]

A moon base by 2050, maybe.
A Mars base by 2100, maybe.
A probe of some kind to every planet and moon in the solar system by 2100? Definitely.
But I don't see manned space flight ever going beyond Saturn. The 17-year voyage to Uranus was too daunting to me, in Orbiter, with a scenario editor:lol:

Still, that's saying alot. So what if we never get beyond Saturn? Being despondent about that is like being depressed because I know I will never have more than about $3 million. I would be eternally happy with far less than that!

I would be thrilled just to see us reach Mars or the asteroid belt, let alone the outer solar system and I don't think that is out of the realm of possibility in oh, say, 200 years

 

[Izack]

I'm not sure if we'll have a Moon base by 2050 or old tales of things called 'rockets,' or even folklore about how the Moon is actually a big rock in space instead of a coin glued to the Firmament. :lol: