Discussion Your Venus/Mars mission concepts/proposals

[Unstung]

The thread is already several pages in, but I think that this concept is worth mentioning (its proposed objectives, payload, and mission design). Maybe it can help you refine the payload and the goals of the mission. The study includes a lander and a balloon. Speaking of landers, the Venus In Situ Explorer is an aged proposal for the New Frontiers program.

UPDATE: I find that a recent blog post by Van Kane is also relevant.

Today, our knowledge of Venus’ surface and its interior is similar to our knowledge of Mars in the 1970s following the Viking mission. The Soviet Union placed several probes on the surface that made simple measurements in the hour or so before the surface heat fried their electronics. NASA’s Magellan spacecraft mapped the surface with radar in the early 1990s at about 120 m resolution globally. We know, however, from our experiences mapping the Moon and Mars’ surfaces that teasing out the details of geologic processes requires mapping surfaces with resolutions less than 50 m resolution with smaller areas mapped at a few meters resolution.

Mapping Venus’ surface (with one exception we’ll return to later) requires using imaging radars that can penetrate its thick cloud cover. The technology in the early 1990s when Magellan flew was relatively new and crude by today’s standards. Now imaging radars are widely used to study the earth both from airplanes and from satellites. The technology is mature and relatively low cost.

As a result, something of a cottage industry has grown up proposing new missions to map Venus either through the European Space Agency’s Medium Class program or through NASA’s Discovery program. The different accounting rules applied by the two agencies make direct cost comparisons difficult, but these missions cost in the neighborhood of $500M to $600M. A Venus radar mapping mission has been proposed for the current ESA Medium Class competition, and I hear that up to three missions are in competition for selection through the NASA program.

The European selection process tends to be more open than the U.S. process, and the EnVision team led by Dr. Richard Ghail at Imperial College London shared a copy of their proposal to ESA with me. The EnVision mission would address several key questions:

• The average age of Venus’ surface is just a few hundred million years old, a tiny fraction of the age of the surfaces of most rocky and icy moons in the solar system. What processes resurfaced the planet? Did they occur in the same time period or have they been spread over time?
• Is Venus currently geologically active and therefore continuing to remake its surface and release new gases into the atmosphere?
• What processes modify rocks once they are delivered to the surface? Venus’ atmosphere is so thick that its surface in many ways is similar in terms of pressure to what is found at the bottom of our oceans. This should lead to complex weathering and erosion, which is consistent with what we saw from the pictures taken on the surface by the Soviet Union’s Venera landers.
• What is the internal structure of Venus like? This is the part of a planet we can never see, but scientists can study it indirectly through the combination of Venus’s gravity field and surface topography. Both were mapped by Magellan, but at too crude of resolutions to answer key questions.

To address these questions, the EnVision spacecraft would carry four instruments.

[...]

 

[ISProgram]

Interestingly, I see only one tank on VESPA-O... monopropellant engine?

Yes, VESPA-O uses monoprop propulsion; six MR-107N engines (just like MAVEN ) which will provide a total thrust of 1,020 N. The earliest concepts of VESPA-O (before the baseline version) were to use a bipropellant engine, the R-4D.

The thread is already several pages in, but I think that this concept is worth mentioning (its proposed objectives, payload, and mission design). Maybe it can help you refine the payload and the goals of the mission. The study includes a lander and a balloon. Speaking of landers, the Venus In Situ Explorer is an aged proposal for the New Frontiers program.

UPDATE: I find that a recent blog post by Van Kane is also relevant.

Well, VFM is the main resource that inspired me to start work on VESPA; I've also heard of EnVision, but since radar mapping isn't currently part of VESPA's mission, I didn't check it out. I do hope that it is approved by ESA, though.

Never knew about VISE, though, until you mentioned it. I'm a little shocked by that one. I'm gonna need a screenshot to show you guys why... :shifty:

---------- Post added at 11:35 AM ---------- Previous post was at 05:28 AM ----------

Okay, so ran into an issue that I should have seen coming; I have to redesign the atmospheric balloon for VESPA-O, as the rescaled aeroshell is too small for VFM's baselined balloon.

The only Venus balloons I know of were from the Vega probes; their balloons were much smaller than VFM and they could POSSIBLY fit in the aeroshell. However, they had a much shorter lifetime than the one I originally intended (~60 hours vs 30 days), and they won't be capable of carrying a lot of instruments.

Because of this, I have two options feasible at the moment:

1) Make the aeroshell bigger to fit the balloon. Well, I made it smaller for a reason...

2) Nix the balloons, or redesign them. I would rather not do either; I would prefer that VESPA-O have a subprobe with it, mainly for logical purposes. Not to good with independent designs either, I prefer to source my data from actual s/c designs.

3) Oh. I guess there is a third option. Um, make Giovanni something less design-risky. Instead of a balloon, go for a atmospheric parachute-dealy! Practically every atmospheric probe is of the parachute design (Huygens, Galileo, etc.), so its not risky at all. There's also data on these probes! The balloon could be moved to VESPA-A, which won't have the same space issues VESPA-O is having.

If all else fails, 3) is what I will probably go with. If VESPA-O has better s/c performance than expected, than I'll go for 1). At the moment, I'm going for 2)...

VESPA-O in launch configuration, within the Verseau fairing:

---------- Post added at 11:44 AM ---------- Previous post was at 11:35 AM ----------

Oh, and with regards to PADSL, a forum is discussing Deimos and Phobos spacecraft. :thumbup:

---------- Post added at 02:19 PM ---------- Previous post was at 11:44 AM ----------

Okay, VESPA-O (needs an official name) will have additional instruments:

Lanqmuir Probe, Magnetometer, and a Ultraviolet Imaging Spectrogragh, are all planned for the baselined instrument suite; the total instrument mass as of now is ~50 kg. A lightning detector is also under consideration.

 

[K_Jameson]

The lightning detection can be accomplished by a RPWS package (your langmuir probe is usually a part of this), as the one mounted aboard Efesto orbiter and various other spacecrafts (Cassini and Galileo had performed lighting detection during the respective Venus flyby en route to its respective destinations). A dedicated lightning detection instrument can be useful in the descent probes.

 

[ISProgram]

It's becoming increasingly likely that Giovanni will become a standard atmospheric probe, with just a parachute. Maximum mass would be 400 kg; 315 kg would be the minimum.

Giovanni is approximately the same size as the Large Probe on the Venus Pioneer Multiprobe, 1.5 m in diameter.

VESPA-O is almost technologically complete...:thumbup:

---------- Post added at 11:21 PM ---------- Previous post was at 10:53 PM ----------

Instead of the UVI instrument mentioned a few posts up, there will be a Ultraviolet Imaging Spectrograph (UVIS) instead...

Not sure if that's basically the same thing, but whatevs...:lol:

Also, I should have the first detailed VESPA post up soon.

 

[Nicholander]

Huh, that's interesting. My Neptune Flyby Probe's Atmo. Probe also has a diameter of 1.5 meters.

Oh, how are you doing to parachute animations for the atmospheric probes? (I think I could use what you're using for my atmo. probe)

 

[ISProgram]

Huh, that's interesting. My Neptune Flyby Probe's Atmo. Probe also has a diameter of 1.5 meters.

Oh, how are you doing to parachute animations for the atmospheric probes? (I think I could use what you're using for my atmo. probe)

Yessss....that's a complete coincidence...

No intentions at the moment for VESPA to be an addon, until I learn how to implement such an addon. For crying out loud, I have difficulty planning TransX flights! TRANSX!

But I will need some knowledge of Spacecraft3 to even consider making VESPA an addon, so at the moment the current discussion is focused mainly on the technical feasibility of the mission. Also, would have to finish making IPSA's launch vehicles so VESPA could launch, but I've run into problems completing it.

 

[Nicholander]

Oh. Sorry, I didn't know that you weren't making the addon yet, just making a concept.

(By the way, I think you should use IMFD instead of TransX, it's easier to use, to me at least.)

---------- Post added at 07:03 PM ---------- Previous post was at 06:44 PM ----------

But, anyway, I think I'll work on PADSL until I either figure out how to do the parachute and such for my atmo. probe, or ask someone to help me make it.

So, the next thing I'll have to do is figure out how big the fuel tanks should be. I used a delta-v calculator, and to get the ~3 km/s of DV required for PADSL, with it's dry mass at 3.2 tonnes and an isp of 330 (The same engine used by all the FOI probes), it would need 4.8 tonnes of fuel. K_Jameson, how big would the fuel tanks have to be? (It's using the same 980 n/330 isp engine that Shakespeare, Efesto and Galileo II uses)

 

[K_Jameson]

Depends on the shape and number of the tanks. Spherical? Two or more?
It's difficult to answer at your question without any depiction of your spacecraft.

 

[ISProgram]

Was going to say something along the line of what K_Jameson said. Just didn't know how to word it.

AFAIK, you're using a bipropellant propulsion system; good Isp compared to monopropellants (hydrazine, etc.), but you just created a huge design issue with the drop tanks. You are going to need separate tanks for the fuel and oxidizer for both drop tanks, as well as the main bus, and that drives up dry mass and design complications.

Also your tank structure;is it the classic shape or is it toroidal? IMO, the latter is better for spacecraft drop tanks, it's less risky to jettison one toroidal tank then it is to jettison two symmetrical "classic tanks"...

 

[Nicholander]

For the size of the tank, the main one inside the spacecraft which contains about ~75% of the total fuel is the same shape as the one in the VESPA-O spacecraft, and the jettison able drop tanks is toroidal, like the drop tank on Phobos-Grunt, and it contains ~25% of the total fuel. (Keep in mind, same FOI probe engine and 4.8 tonnes of fuel)

 

[ISProgram]

But there's the problem: VESPA-O main prop tank holds about 1,640 kg of hydrazine monopropellant (same as MAVEN). The FOI probes use a bipropellant, though I'm not sure about the combination, probably NTO/MMH. Bipropellant engines have a better Isp than monopropellant engines; this is why VESPA-O has a ME Isp of 232, but Efesto has one of 330, bipropellants are more efficient.

And there's the fundamental problem. Instead of one tank for the monoprop, you'll need TWO tanks to carry each prop for the biprop. So, a toroidal tank isn't an (simple) option anymore, it needs to hold two propellants, if it's jettisonable, you'll need a separate tank (not necessarily toroidal) for the other propellant component.

Case in point:

Biprop is left, monoprop (VESPA) is right.

 

[Nicholander]

Okay, sorry, I meant to say that there were 2 tanks that were the "Pill" like shape similar to VESPA-Os. But, couldn't you have 2 toroidal tanks, one having the N204, and the other containing the MMH?

 

[ISProgram]

:facepalm: Um...wow. That was stupid of me.

Erm, back to the point, it is possible to stack a toroidal tank on another toroidal, but that poses problems with jettison, at least how I see it. IMO, I think that setup might be a lot of mass you don't need, but that's just me.

On the bright side, depending on the O/F ratio of the biprop engine used by the FOI probes, both tanks can be identical in size, so that simplifies calculations.

But your main probe holds 75% of the total fuel, so that's about 3,600 kg of fuel. That JUST might be doable, some geosats can manage that, but it almost negates the need for a drop tank.

For comparison, a Briz-M holds about 19,800 kg of fuel, but only 5,800 kg of this isn't in the drop tank it utilizes. That's 1/3 of it's total fuel mass; the drop tank holds the other 2/3 of the fuel. PADSL's drop tank would only hold 1/4 of the full fuel mass, and the drop tank the other 3/4. This trend should be reversed...

Another point. Compared to VESPA, PADSL is big. VESPA manages 1/2 the prop mass PADSL needs with just its single tank. PADSL shouldn't even need a drop tank.

 

[K_Jameson]

In fact, even a single toroidal tank can hold a bipropellant combination; just make a "common bulkhead" inside the torus, so the fuel is in one half and the oxidizer in the other half. Look at this cross section of a Breeze M rocket stage:

Surely, common bulkheads adds complexity, risks and increases the costs. I have not seen many space probes with common bulkhead tanks...

 

[Nicholander]

So a single toroidal tank can hold bipropellant, but, back to the point, so if we has the main fuel tank have 40% of the fuel, and the toroidal drop tank have 60% of the fuel, using the N204/MMH fuels, how big would the fuel tank be? (By the way, the diameter of PADSL is 3 meters in diameter, so keep that nonmilitant in mind)

 

[ISProgram]

Wow...forgot the Briz-M is bipropellant. :facepalm:

Sorry to answer a question with another question, but what's the O/F of the main engine? Maybe K_Jameson has an answer to that.

Without it, we can't calculate individual prop loads for the seperate fuel compartments. If I get that, I could give an answer.

 

[K_Jameson]

Just for reference, this is the tank arrangement of Shakespeare:

980 Kg. N2O4/MMH. Oxidizer/fuel ratio: 2.16. Propellant is in the two spherical tanks at the center. Laterally, we have two helium tanks for fuel pressurization, and the spherical backup hydrazine tanks for the RCS engines.

 

[ISProgram]

And now I need <10 minutes....

 

[K_Jameson]

You need even the density of oxidizer and fuel, that is 1.450 g/cc and 0.880 g/cc, respectively.

http://www.astronautix.com/props/n2o4mmh.htm

 

[ISProgram]

Okay, so PADSL has 4800 kg of fuel, the main tank has 40% of that.

That means it holds JUST 1920 kg of prop. So 608 kg of MMH (fuel), and 1312 kg of N2O4 (oxidizer).

The density of N2O4 is 1.44246 g/cm3 , MMH is 880.00 kg/m3. Using this calculator, the volume for each prop is 26.83 ft3 (N204) 32.12 ft3 (MMH).

The tanks are now more or less the same size, just adding an extra 5% of volume for ullage should give you the actual volume of the tanks. That's 33.72 ft3 volume for the largest tank, and both tanks are essentially the same size, so there, you clone the tank even for the N204, even though it'll take up less space.

---------- Post added at 09:36 PM ---------- Previous post was at 09:35 PM ----------

Yes. :hesaid: