Talk:Single-stage-to-orbit
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The first part of this is about the DC-X experimental vehicle. This is an interesting topic and Wikipedia should have an article on it. But why is it HERE? The connection of DC-X to single stage to orbit is rather tenuous. DC-X never made orbit and was not intended to. The intention was to test new technologies that are rather neat, but have no obvious connection to SSTO.
The article doesn't even define what single stage to orbit means. It only briefly and peripherally explains why it might be a good idea. It doesn't discuss any of the difficulties with the concept, and there certainly are difficulties, at least in the minds of the guys who sign the checks. We have being doing orbiters for 40 years with a great variety of hardware, and NONE of it was SSTO.
For all these very serious criticisms i get the feeling the author still knows more about the subject than i do, so i'm not going to jump in and fix it just yet. But someone, please do.
Material from SSTO, take what you need:
Short for Single Stage to Orbit. In contrast to multistage rockets, the whole vehicle reaches orbital velocity. It is believed that SSTOs would led to much reduced costs for the access to space and allow aircraft like operations. The main problem in constructing such a vehicle is to make the engine efficient and the vehicle structure lighweight enough to avoid carrying excessive amounts of fuel or to be forced to drop away parts of your rocket while in flight. All attempts in constructing such a vehicle (DC-X, Roton, X-33) have so far been unsuccessfull due to technical and/or economic difficulties.
I do not see any discussion of Space Ship One...
- At this point, SS1 is neither Single-Stage (carried initially by White Knight aircraft) nor Orbital. Lomn 21:38, 2 August 2005 (UTC)
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[edit] Article needs rewriting
Appreciate the effort that's gone into this article, but it has quite a few grammar and writing style problems. Some Wikipedia style guidelines: [[1]]. There are also several misleading or speculative statements not appropriate for an encyclopedia. Examples:
"The lack of such abort modes on the Shuttle requires incredible failure avoidance costs and massive overhauls", given in the subheading "Why SSTO". This is wrong for several reasons: (1) The shuttle has many abort modes (2) The relationship of abort modes to SSTO is tenuous and shouldn't be listed in this subheading. The conventionally staged Soyuz is listed, which is a non sequitur, tangent to the subheading topic.
Another example: several "conventional wisdom" statements about the space shuttle are speculative and of uncertain veracity. E.g, "...high cost per launch of the Space Shuttle (a vehicle ironically designed to reduce launch costs)." Testimony of key shuttle officials during hearings by Columbia Accident Investigation Board indicates that's not the case. Operational costs were not unexpectedly high, but largely in line with early estimtates. For an actual transcription of relevant testimony, see [2]. There is a difference between conventional wisdom popularly repeated in the press and actual facts. Encyclopedias should strive to stick to the facts.
"The final vehicle required massive amounts of maintenance after every launch. This shift was partly a result of the removal of various abort systems, requiring the vehicle to be made safe via intensive inspection." This seems speculative. What abort systems were removed? What is the source for stating the lack of abort systems is directly related to operating costs? How would an abort system (e.g, launch escape) have sufficiently decreased inspection requirements to make a significant difference in operating costs?
"The engines are removed and rebuilt, large amounts of the structure are taken off for testing, and the entire refurbishing cycle takes months." The engines are not rebuilt after each launch, they are inspected.
I'd also suggest a link to Tsiolkovsky rocket equation, along with simplified explanatory verbiage, as this is the underlying technical reason why SSTO is difficult.
I'll be happy to rewrite the article if you agree and think it would be beneficial. My goal would be to retain most of the current material, better adherence to Wikipedia style guides, elimination of problem areas like the above, and addition of some clarifying material. Joema 17:19, 29 December 2005 (UTC)
[edit] Article now rewritten
I've essentially rewritten the entire article to improve readability, remove numerous inaccuracies and POV statements. Encyclopedia articles should be non-judgmental and mainly descriptive information about the topic. Following the principles in The Elements of Style will greatly improve clarity. It's especially important to avoid unnecessary words and sentences. Don't use passive voice, and avoid long prepositional phrases. To quote The Elements of Style: "A sentence should contain no unnecessary words, a paragraph no unnecessary sentences, for the same reason that a drawing should have no unnecessary lines and a machine no unnecessary parts." See http://www.crockford.com/wrrrld/style3.html#13.
[edit] More work needed
I agree with Wolfkeeper about article needing more work. Starting that work now.... Joema 22:51, 9 February 2006 (UTC)
- As suggested, I've made numerous improvements. Reducing word count improves readability, yet doesn't require sacrificing meaningful content. See Elements of Style. In particular, see: [3].
- Other contributors: please discuss here any issues with the changes. Joema 17:25, 10 February 2006 (UTC)
[edit] Dense vs Hydrogen Fuels
"The end result is the thrust/weight ratio of hydrogen fueled engines is 30-50% lower than comparable engines using denser fuels.
This inefficiency indirectly affects gravity losses as well; the vehicle has to hold itself up on rocket power until it reaches orbit. The lower thrust of the hydrogen engines means that the vehicle must ascend more steeply, and so less thrust acts horizontally. Less horizontal thrust results in taking longer to reach orbit, and gravity losses are increased by at least 300 meters per second. While not appearing large, the mass ratio to delta-v curve is very steep to reach orbit in a single stage, and this makes a 10% difference to the mass ratio on top of the tankage and pump savings." Shouldn't the hydrogen vehicle be the one that actually has a higher t/w ratio and lower gravity losses? Even if the engines have 30-50% lower thrust, hydrogen is so much lighter than RP1 that there should be more than 50% reduction in the total vehicle mass.
As it is now, this section does not seem very NPOV. It concentrates on the advantages of kerosene while ignoring many of the advantages of hydrogen. It also seems to imply that some dense fuels are better hydrogen for SSTOs, even though many studies concluded that hydrogen is the best option.--Todd Kloos 05:07, 25 March 2006 (UTC)
- [Disclaimer: IANA Rocket Scientist]
- I believe the quote is correct[4]. H2/O2 has a higher I_sp, but higher ΔV to orbit.
- —wwoods 09:54, 25 March 2006 (UTC)
[edit] Minor Clarification suggested
... the lower lunar gravity and relatively thin atmosphere makes this much easier than from Earth.
This sentence should be rephrased for accuracy - the moon has practically no atmosphere. According to the Wikipedia entry, lunar atmospheric pressure is only 3 × 10-13 kPa. Calling this near vacuum a "relatively thin atmosphere" sounds like a tortured euphemism.
Textor 06:10, 25 April 2006 (UTC)
[edit] specific impulse
The section on dense vs. hydrogen fuels uses the units of 'seconds' in reporting specific impulse. The measure is of impulse per unit mass so the number is about 9.8 times higher in SI. The numbers given are for pounds-force seconds per pound mass. In SI the metric is Newton-seconds per kg. The article on 'specific impulse' is similarly unclear on this point. 4.232.3.182 17:02, 15 August 2006 (UTC)
- Trolling can be fun can't it? Anyway, pounds-force seconds per pound mass is heavily deprecated here, and *very* rarely used elsewhere. Newton-seconds per kg (or m/s) is acceptable, when accompanied by the Isp in seconds. But seconds is actually correct in both metric units and non metric units, the defining equations can be found in most textbooks.WolfKeeper 18:32, 15 August 2006 (UTC)
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- Competent rocket engineers know that the definition of specific impulse is the impulse delivered per unit mass of propellant expended; thus the name. Competent rocket engineers also know that the correct units for specific impulse are lbf-sec/lbm in U.S. units and N-sec/kg in SI. If they are old enough they may even know how the erroneous units of seconds happened. 4.232.0.191 13:47, 22 August 2006 (UTC)
[edit] Ratios
The ratios discussed in the "Why SSTO?" section are incorrect. A 2 to 1 ratio would be 2 parts of "X" and one part "Y", not one-to-one as stated in the article. The other ratios are wrong, too. A 5 to 2 ratio is 28.6%, not 40%, and a 4 to 1 ratio is 20% not 25%. I would correct it, but I don't know the actual fuel to structure ratios of the aircraft. Does the stunt plane really have a 4 to 1 ratio structure/fuel ratio (20%) or is it 25% fuel (3 to 1 structure/fuel ratio)? Martylunsford 15:17, 30 October 2006 (UTC)
Dunno about those in particular, but you're definitely wrong about your ratios for this article. Check out mass ratio; it points out that in rocketry, the ratio that is important is m0/mf (m0 is the initial takeoff weight, and mf is the final weight when the rocket ends its burn). As you can see a 4:1 ratio (m0/mf) is 25% dry weight. That ratio is also important in aircraft for calculating range. In both cases the ratio is not the ratio of fuel to structure; that's mathematically awkward for rocketry and aircraft range calculations and is never used (not without an explicit label anyway).WolfKeeper 18:36, 30 October 2006 (UTC)
I changed it anyway, it's more accurate and less confusing to have dimensionless number. That's the way Sutton does it.WolfKeeper 18:55, 30 October 2006 (UTC)
