Why was the space shuttle retired without an immediate successor?

[Stranger_On_A_Train]

@Earl_Snake-Hips_Tucker

The article didn’t mention exactly why SLS was limited to every six months, but I guess part of it is we just don’t have an assembly line popping them out like soft drinks.

I don’t have an intimate knowledge of the SLS, but my guess based upon what I do know of STS processing is that it is a combination of manufacturing of the Stage 1 tankage and structure at Michaoud and the processing time at the Cape, which is enormously labor intensive. There may also be delays in the manufacture of the Solid Rocket Boosters due to limited availability of the propellant constituants, which are not longer produced in the requisite volume on a regular basis.

@Learjeff

I bet guys like Stranger could go on for quite a while on what makes space flight more than just another engineering problem. Some day, sure, but today it’s still at the very edge of feasiblility.

You’ve pretty much summarized it; even though the materials and processes used in a lot of rocket launch vehicle applications have been around for a long time and are reasonably mature, they are still stressed to the edge of structural and thermal capability in an application where a single failure could result in catastrophic loss of vehicle, payload, and mission.

However, there are certainly things that can be done to reduce both complexity and improve effective reliability while substantially reducing costs. Separating personnel launch vehicles and heavy lift vehicles is certainly one way to go that allows you to emphasize reliability and reusability for a smaller system (at the expense of cost), while accepting lower reliability and performance for an expendable heavy lift system. Even partial reusability of a lower performance heavy lift vehicle is plausible; see Bob Truax’s Sea Dragon concept. Unfortunately, the SLS is essentially a Shuttle-derived vehicle with all the baggage that brings and doesn’t take advantage of any significant means to reduce processing or labor costs.

Stranger

[AdamF]

@Stranger_On_A_Train

You are correct that NASA is being given the mandate to maintain some kind of crewed program–whether it makes sense in terms of scientific and exploratory research or not–but even given that, the SLS is suboptimal. For one, it makes the same mistake as the STS in trying to combine heavy lift and crewed capability, which combines high performance (in terms of absolutely payload) with a high degree of redundancy, which are often competing objectives. A better configuration would be a lower propulsive performance heavy lift vehicle with a somewhat reduced expected reliability with a compact crew-only launch and return vehicle intended for deliverying crew to a space station or transfer space craft. The cost/benefit of this is clearly demonstrable, but it would require the development of two parallel systems which NASA cannot afford, and the safety culture of NASA will not accepted reduced reliability even in a cargo-only vehicle despite that it could potentially reduce both development and launch costs by an order of magnitude.

I agree 100%. Something the size of SLS will definitely be needed for any manned mission to Mars, and probably even for a mission to an asteroid. Falcon Heavy may work, but it’s a bit small and the estimates sound rather optimistic. But SpaceX Dragon would be perfectly suitable for lifting the crew to a waiting spacecraft in the low orbit. It may even be good enough for re-entry at the end of the mission.
Orion is also part of the problem. The whole multi-purpose design requirement turned it into a white elephant. It’s a jack-of-all-trades, but master of none. Great if NASA was planning a large manned exploration program to multiple targets, but that’s not going to happen.

[bossy]

@aNewLeaf

I’m a programmer by training, we studied that in school.
The software for the Space Shuttle, orbiter, ground, the whole package- is the grandest software engineering project in history.
It’s error free. There are no errors in the code, every single bit has been interdependently analyzed and cross checked and reverified.
It’s flawless. It’s legendary. It’s the Hoover Dam of software.

Not quite the Hoover Dam. At least 18 software errors found following an unscheduled simulation: http://www.cs.berkeley.edu/~bonachea/294-8/hw1.html

[Elendil_s_Heir]

@Elendil_s_Heir

Wiki says otherwise; the last known NRO launch was in Sept. 2012, and there are at least 11 more planned: List of NRO launches - Wikipedia

One of which was just today: http://www.cnn.com/2013/08/28/us/spy-satellite-launch/index.html?hpt=hp_t2