Larger Boosters...

[rocketman5000]

I had a quick thought while sitting today at lunch surfing the net. In particular I was reading about the flight profile of the Messanger spacecraft and how many flybys that it would have to complete in order to enter Mercuian (?) orbit. <br /><br />If a larger booster was available that could impart more dV to a spacecraft and minimize the need for flybys to increase its speed would it be worth the extra money in turn for reduced mission duration? <br /><br />My assumptions were that you are paying an annual wage for the scientists overseeing the mission. If the mission could be completed in less time would there be a financial gain from reduced manhours even after accounting for the extra expense of the booster?

 

[larper]

The driving cost of space exploration is the cost to orbit. So, every ounce that you can squeeze into a mission gets you the most long term savings.<br /><br />So, if you increased the size of the booster, the mission team would use the increased performance to add more capabilities to the spacecraft, not adding fuel to decrease the mission duration. So, you would still be doing all of the flybys, just with a bigger spacecraft. <div class="Discussion_UserSignature"> <p><strong><font color="#ff0000">Vote </font><font color="#3366ff">Libertarian</font></strong></p> </div>

 

[nyarlathotep]

If booster costs per pound were a tenth what they are today, I'm not so sure that would be true. <br /><br />There are tangible fiscal and opportunity costs in having the group of scientists which designed the mission sitting around for an extra year twiddling their thumbs waiting for that extra flyby before getting their data. At some point that cost has to start exceeding that of an extra 3000m/s of dV.

 

[PistolPete]

I think that this is due to how much money is set aside in the program budget for launch vehicle cost. There are plenty of LVs that can lift large payloads into an earth escape trajectory, but most of these probes are built on a very limited buget so they can't afford such large LVs such as the Delta IV Heavy. Most of the time, they try to squeze as much developmental dollars as they can from the buget (you want it to work right the first time don't you?), so they end up skimping on LV cost and try to cram as much as they can on a relatively cheap Delta II. This is why these kind of probes have to do seemingly countless flybys to gain as much free delta v as possible. <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[vogon13]

The bigger booster would have been largely used to loft more fuel to Mercury for the orbit insertion manuever. Seems interesting and practical to try out the multi-encounter flight plan to Mercury.<br /><br />After all, the trajectory is reversible for a future sample return mission . . . . <br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[spacester]

I once noodled with the numbers to orbit Mercury on a quicker timeline, IOW without all the flybys.<br /><br />The conclusion was clear in my mind: what is needed is <b>more stages</b>, not just more mass to LEO. <br /><br />Using the same total impulse to impart more dV to a lighter craft is not the answer because of the enormous dV still needed after you've departed the Earth's gravity well. <div class="Discussion_UserSignature"> </div>

 

[gunsandrockets]

A bigger booster is not the easiest way to increase the speed of an interplanetary spacecraft. What you really need is a more efficient Earth escape stage. It's a case of a little goes a long long way.<br /><br />For example the mighty Soviet N-1 'moon rocket' (really a Mars rocket) was twice the size of a Saturn V, yet the N-1 could only propel 2/3 as much mass on a lunar mission. Why? Because the Saturn V's final stage used the very efficient liquid hydrogen + liquid oxygen burning J-2 rocket engine. The N-1 rocket by comparison burned kerosene + oxygen. The more efficient Saturn rocket engine made all the difference.<br /><br />So instead of using a big ass booster, what you want is a better rocket engine on the final stage of the booster. Some possibilities are nuclear rockets, solar thermal rockets, or electric rockets.

 

[subzero788]

"...the mighty Soviet N-1 'moon rocket' was twice the size of a Saturn V.."<br /><br />Sorry to get technical but that's simply not correct: the Saturn V was about 20ft taller. The N1 did produce more thrust but only about 1/3 more than the Saturn V (~10 million pounds vs ~7.5 million pounds IIRC).

 

[nyarlathotep]

The problem with the N-1 rocket wasn't the choice of fuel. The fact that you can buy a Zenit, Soyuz and Proton for a fifth of the price of an American LH2 powered vehicle makes this obvious. N-1 went wrong because the program was massively underfunded (in PPP terms the rocket had less than 1/10th the funding of S-V) and vital testing which could have discovered destructive vibrational modes and exhaust fluid dynamic problems was skipped. <br /><br />Had funding been continued after Apollo 11 and the niggles worked out, I have no doubt that the N-1 would have made a magnificent vehicle. Even today the NK-33 and NK-43 engines developed for the program remain the highest performance Lox/RP1 engines on the market. <br /><br />"Sorry to get technical but that's simply not correct: the Saturn V was about 20ft taller. The N1 did produce more thrust but only about 1/3 more than the Saturn V (~10 million pounds vs ~7.5 million pounds IIRC)."<br /><br />The N1 was slightly larger by dry mass. 208900kg vs ~190500kg for the Saturn.

 

[barrykirk]

So the N1 was denser than the Saturn V... Well hydrogen has a very low density.

 

[nyarlathotep]

The larger more fragile H2 stages also create problems with assembly. Fuel is dirt cheap, who cares if we use twice as much.

 

[barrykirk]

Well, I'm a big RP-1 fan....<br /><br />There are a number of problems with H2.<br /><br />For the booster stage, RP-1 is unquestionably the better than LH2. As for upper stages... it could go either way.

 

[rocketman5000]

Agreed, LH2 leads to size issues espically with lifting bodies, but for upper stages which needs far lower mass of propellant you can still sit a sizeable tank atop the stack without impeding launch dynamics.

 

[willpittenger]

I do have to note here that a single F-1 had more thrust than the entire J-Mission Apollo/Saturn stack, excluding other F-1s. I am including every last thruster. Even those used for manuevering and braking are included.<br /><br />That's powerful. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[PistolPete]

Yes, but thrust isn't even the main factor (or even a major factor) in the rocket equiation, Isp is. <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[propforce]

Before I address the cost aspect, let me first address the performance aspect of what is needed for a launch vehicle.<br /><br />Anyone who has driven a stick-shift vehicle (on the ground) can relate to this. In order to move a heavy payload for a long distance without refueling requires the following capabilities<br /><br />1) Torque (as function of engine horse power and gear ratio), and<br /><br />2) high mileage per gallon (mpg) fuel efficient vehicle, or<br /><br />3) a large gas tank if the mpg is not upto par<br /><br />If the engine mpg is not too good, then you'll basically need an 180 wheeler to drive cross-country with no payload. It's effectively hauling its own gas tank. But you also need the horsepower (torgue) to get the vehicle going (at 1st gear) and, as the vehicle accelerate, less power is required to keep it going faster (hence shifting to over-drive gear).<br /><br />You also noticed that there seems to be a correlation between the horse-power of a vehicle and it's fuel efficiency. Being a brilliant analyst, you puzzle over the fact that there seems to be no 18 wheeler available that can go 200 mpg. You can't put your fingers on why this is, but you grudgingly acknowledge that there's either a law of physic or a law of economic that dictated as such, so you shurg and move on with your design.<br /><br />By this time, some smart people would say "hey, wait a minute!... I don't want this 18-wheeler to go across country! I want a 3-stage vehicle! So instead of the 18 wheeler needed for a 1st stage, I can get away with a Chevy 350 instead (cheaper), the 2nd stage can be a Chrysler mini-van, and the 3rd stage can be a Toyota hybrid !!...."<br /><br />Well, that makes a smarter sense I'd say, as you "shed weight after each stage" effectively making the overall vehicle smaller and less expensive. But remember, a Toyota hybrid doesn't carry a lot of "payload". So if you want something bigger than a Toyota hybrid can carry, then you'll need to get back to revi <div class="Discussion_UserSignature"> </div>

 

[barrykirk]

PistolPete,<br /><br />Actually thrust is a much more major factor in the rocket<br />equation than you would think. <br />It's an indirect factor, but a very significant one.<br /><br />Or to be more precise, it's thrust to weight ratio.<br /><br />The rocket equation goes as follows.<br /><br />Delta V = ISP * ln ( initial total mass / final total mass )<br /><br />Obviously, the ISP is a direct multiplier for the Delta V<br />and is a very important factor.<br /><br />However, when lifting off from the earth's surface it<br />takes a certain amount of thrust to get the rocket off the ground. <br />The thrust of the engines must be greater<br />than the weight of the rocket plus fuel or your not going<br />anywhere until you burn off some fuel.<br /><br />Let us say for arguments sake that I'm able to double<br />the thrust of my engine without changing anything else <br />including ISP. Well that means I can double my initial<br />total mass. Let us say that we've doubled the initial<br />total mass but left the final total mass the same.<br /><br />Well than my Delta V has gone up by 43%!!!<br /><br />So, with the same ISP, I've gained a Delta V of 43%.<br /><br />Doubling the thrust is not as efficient as doubling the<br />ISP, but it certainly is a major factor.<br /><br />Now this argument makes the most sense for booster<br />stages... Once your already in LEO, thrust to weight<br />ratio beyond a really small value is meaningless. At<br />that point ISP is the most important factor.<br /><br />The highest ISP non nuclear engine and practical rocket<br />engine we have that can lift itself off the ground is<br />LH2 / LOX. Sadly, the thrust to weight ratio's of these<br />engines isn't that great. <br /><br />Even worse, LH2 is very low density and it's highly<br />cryogenic and low viscosity. LH2 tanks are the heaviest<br />fuel tanks for any fuel that we use. Now, the space<br />shuttle main fuel tank is incredibly light weight for what<br />it is, but it's probably twice the weight and size of

 

[josh_simonson]

>The driving cost of space exploration is the cost to orbit.<br /><br />Actually the cost of spacecraft is generally several times the cost to launch them. The mars rovers together costed $800M, but the two delta 2 launches that sent them on their way only cost perhaps $120M combined - only 1/6 of the cost. The cost of launching most spacecraft is actually insignificant, and that's why the demand curve is so flat for spacelaunch. Even if Delta 2s were free, the MERs would have cost less than 20% less.

 

[barrykirk]

I've heard that several times.<br /><br />Why is that so?<br /><br />If weight were not an issue, would it be possible to build a spacecraft with the same capabilities but at a fraction of their current cost?

 

[qso1]

Weight is a factor to be sure but much of the cost of spacecraft is tied up in technical expertise and the fact that spacecraft are not mass produced in large enough numbers to take advantage of economies of scale. The MER rovers are most likely going to be the only two identical flight rovers that will ever be built. Viking craft, two orbiters and landers of a kind. Pathfinder...one of a kind. Finding a way to mass produce spacecraft should reduce cost in addition to trimming the mass down. But in reality, given the other problem, its a government operation...the cost would probably be about the same.<br /><br />Having said all that, the cost of mars exploration has actually come down from the Viking and Mars Observer days. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[gunsandrockets]

...the mighty Soviet N-1 'moon rocket' was twice the size of a Saturn V.. <br /><br />"Sorry to get technical but that's simply not correct: the Saturn V was about 20ft taller. The N1 did produce more thrust but only about 1/3 more than the Saturn V (~10 million pounds vs ~7.5 million pounds IIRC)."<br /><br />Okay let's get technical. I was refering to mass not height when talking about the N-1. Even so the broader point remains, I was incorrect about the mass of the N-1. After double checking I discovered to my suprise that the N-1 actually masses a little less than the Saturn V rocket.<br /><br />I knew the N-1 had a lot more thrust than the Saturn V and I just assumed the mass of the N-1 was proportionate to the difference in thrust.

 

[gunsandrockets]

"The problem with the N-1 rocket wasn't the choice of fuel. The fact that you can buy a Zenit, Soyuz and Proton for a fifth of the price of an American LH2 powered vehicle makes this obvious."<br /><br />Actually for the original question of speeding up an interplanetary probe, propellant choice is the problem and the N-1 is an example of the wrong propellant choice. <br /><br />"where the N-1 went wrong because the program was massively underfunded (in PPP terms the rocket had less than 1/10th the funding of S-V) and vital testing which could have discovered destructive vibrational modes and exhaust fluid dynamic problems was skipped. Had funding been continued after Apollo 11 and the niggles worked out, I have no doubt that the N-1 would have made a magnificent vehicle."<br /><br />The development bugs of the N-1 was why it never had even one successful flight. But even if it had flown successfully and achieved all the goals for which it was designed the N-1 would still have fallen tremendously short of the performance of the Saturn V.<br /><br />The N-1 was handicapped by the low ISP of the oxygen/kerosene propellants used in it's upper stages. Even though the N-1 used more staging than the Saturn V thereby increasing the mass ratio (and complexity) of the N-1, the Saturn V could send 47 metric tons to the moon and the N-1 could only send 30 metric tons.<br /><br />Or let's put it in the sense of the original question, a fast interplanetary probe. Let's make the probe a massive 30 tonnes, the same mass as the Soviet plan for a manned Mars flyby mission. According to my rough calculations the N-1 would send the probe out at a speed of 3 km/s, wheras the Saturn V would send the same probe out at 4.3 km/s. That's demonstrates the big advantage hydrogen propellant has over the lower ISP of kerosene.

 

[halman]

BarryKirk,<br /><br />Imagine that General Motors waited until a customer had ordered a car before they started building it. And each car was individually made, with only loose specifications as to frame, suspension, and body. No assembly line, all work done by hand. How much would a new Chevrolet cost?<br /><br />This is the situation with the launch vehicle industry right now. Because there is no large demand for launch capacity, the boosters are built one at a time, by hand.<br /><br />Until such time as someone orders a large number of boosters, the unit costs are going to remain high. Once we begin production on an assembly line basis, the unit costs will drop significantly. All we need is for NASA to admit that it will need 30 or 40 boosters of various Atlas configurations, say, and order them in advance, and the assembly line would be set up. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[willpittenger]

Your post doesn't match the post you replied to. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[propforce]

<font color="yellow">Your post doesn't match the post you replied to. </font><br /><br />Please read it again. Not only did it address PistolPete's statement, it addresses various points other posters have as well.<br /><br />But it's written in "parables" so you'll have to read it careful. It contains gems and pearl of wisdoms, I am rather proud of myself today <img src="/images/icons/cool.gif" /><br /> <div class="Discussion_UserSignature"> </div>