Recap
After a general discussion of the fallacy of trying to use the prize concept to advance commercial human spaceflight, I started a series of postings focused on the Cheap Access to Space (CATS) draft legislative proposal to implement such a prize concept. The full text of the CATS’ draft description is available here and the draft legislation here.
My first first critical posting on CATS looked at the entire prize proposal from with a “God’s eye” perspective of how America is to become a true commercial human spacefaring nation. Will the CATS proposal actually accomplish anything useful in this regard? My opinion is that it would not because it only focuses on one functional element of the integrated human spacefaring infrastructure America now needs to build to open the Earth-Moon system to routine commercial human spacefaring operations. The need for integration is clear. Otherwise, the safety, operational utility, and economic attractiveness of the infrastructure is put at risk.
I also returned to my general criticism that the prize approach has not proven successful in commercial human passenger suborbital spaceflight. Hence, why should this approach now be seen as likely being successful for an even greater technical challenge?
My second critical posting focused entirely on the issue of passenger spaceflight safety in the absence of this being addressed in the draft enabling legislation. The success of any transportation infrastructure hinges on the public acceptance of the safety of the passengers. A transportation infrastructure is not a thrill ride. Unfortunately, the draft enabling legislation proposes to treat commercial human spaceflight as a thrill ride or, more specifically, adventure travel such as white-water rafting.
Most people do not understand that the term “passenger” has a specific legal meaning with respect to safety. (Note that I am not an attorney so these comments reflect my understanding.) A passenger is someone contracting with a person or company to be transported to a destination. By law, the person or company providing the transportation has a clear “duty to care” legal obligation to protect the safety of their passengers. A fault with the CATS draft legislation is that it appears to go out of its way to avoid discussing the safety of the passengers or even to acknowledge clearly that passenger commercial spaceflight is being addressed. Instead, the draft legislation appears to try to legally treat humans participating not as “passengers” but as “participants” in adventure travel where the legal burden of protecting their safety falls on the participant. Further, instead of addressing passenger spaceflight safety, the draft legislation focuses on the term “fully-reusable” and tries to imply that this is a suitable replacement term for passenger safety. This is inappropriate for the reasons discussed in the second posting.
In this third critical posting, deficiencies in the draft enabling legislation pertaining to the impact of excluding the Thermal Protection System from the definition of Reusable Launch Vehicle and how the payload requirement is defined are addressed.
Pertinent requirements and definitions from the draft legislation
Section 3, Definitions:
(2) Reusable Launch Vehicle (RLV) shall be any vehicle which is used to propel a crew and cargo into a low Earth orbit, the primary components of which, including but not limited to, rocket engines or other propulsion engine systems, and airframe or similar structures, shall be re-used for each flight.
(3) Line Replaceable Units (LRU) shall carry the meaning and intent as expressed in the Defense Acquisition University Glossary (2015), defined as “An essential support item removed and replaced at field level to restore an end item to an operationally ready condition”, shall be similar in operational concept to the term Line Replaceable Unit as utilized by the United States Air Force in operational high-performance aircraft, and shall be further defined by the Secretary when promulgating rules.
(4) Minimum Required Orbit (MRO) shall be at least 400 kilometers altitude, circular, at 51.6 degrees inclination.
(Note: Modern aircraft are designed to enable many components to be easily replaced when the component fails. For maintenance planning purposes, each of these components is given a designation indicating where the equipment and the technical skills should be available to replace that component. The term “Line Replaceable Unit” refers to parts of the aircraft that are normally replaced all at the same time. A radio is an example. Once removed, the inoperable radio is returned to a depot for repair. Thus, the designation Line Replaceable Unit has no bearing on the flight-safety critical designation of that component. Some are flight-safety critical while others are not. Hence, the inclusion of this definition does not appear to have any clear purpose as this is just how modern flight systems are designed and maintained.)
Section 4, Award Program General Requirements:
1 (a) Transportation of a payload of at least 1 metric ton, including 2 crew members, to the Minimum Required Orbit, using a Reusable Launch Vehicle, where it will complete at least one complete orbit of the Earth, and then return safely to the surface of the Earth.
1 (b) Within 1 week of returning from the Minimum Required Orbit, repeating the requirements specified in subsection 1(a) of this section, using 100% the same Reusable Launch Vehicle, equipment, and systems, as measured by dry mass; or
1 (c) Launching to the Minimum Required Orbit, and returning to Earth, 10 times within 10 weeks of the first launch as specified in subsection 1(a) of this section, and repeating the mission requirement each time as specified therein, using the same Reusable Launch Vehicle, equipment, and systems, as measured by dry mass.
Inadequacy of defining a Reusable Launch Vehicle to not necessarily include the Thermal Protection System
In any transportation infrastructure, the essential elements for safety are reusable. Certainly, some components experience wear or corrosion that periodically require them to be replaced, with brakes being a very good example. But from trip-to-trip, however, the intent and, for the certification of these transportation elements to ensure passenger safety, there is no acceptance of the need to replace these parts after each trip. This violates the airworthiness approach used for certification.
Imagine, for example, trying to certify the safety of an elevator system where the cable needed to be replaced every time the elevator went to the top floor and then descended back to the lobby. Imagine if someone tried to define the reusable elevator system as being everything but the cable. With the cable being essential, such a proposal would not make any sense, would it? Reading such a proposal would cause one to scratch their head trying to understand why such a non-conventional proposal was being made.
Effectively, this is what the draft enabling legislation is trying to do by defining the Reusable Launch Vehicle to exclude the Thermal Protection System. For an Earth-to-orbit-and-return spaceflight system, the Thermal Protection System is a safety-critical element of the flight system. The spaceflight system will not survive reentry absent a functioning Thermal Protection System. The Thermal Protection System (or pieces of it) may, through good engineering, be removable and replaceable as a Line Replaceable Unit, but this does not change the fact that is it safety-critical. If, then, the conditions for winning this prize can be done with one safety-critical element being permitted to be replaced after each mission, why stop there? Why not let the airframe be replaced after each mission? Let all the engines be replaced after each mission? Why not just let an entirely non-reusable spaceflight system win the prize? These would void the focus on demonstrating a fully-reusable flight system.
Clearly something is amiss with this Thermal Protection System exclusion. Such a system will not be fully-reusable, just as the station shuttle system was not fully-reusable because it depended on expendable flight-critical elements. This Thermal Protection System exclusion would appear to arise from the anticipation that a particular spaceflight system design—one, apparently, not fully-reusable—should be permitted to win the prize despite the clear focus of this prize on demonstrating full reusability. In other words, it appears that an anticipated deficient approach is being given a pass.
I think it’s perfectly fine to permit parts—repeat, parts—of the Thermal Protection System to be replaced when there is clear evidence of unexpected wear or damage. However, to be consistent with the clear intent of the prize, the requirement should be that no one part of the Thermal Protection System can be replaced more than one time during the ten missions required to satisfy the prize. The remaining parts of the Thermal Protection System should last the entire 10 flights without any need for replacement.
The same part replacement requirement should then be applied to all other elements of the flight system to maintain consistency. Being able to show that the pending failure of a Line Replaceable Unit can be detected and replaced and still maintain an aggressive flight schedule of one flight per week would be a significant accomplishment. In fact, it may be worthwhile to require that this ability be demonstrated for a main engine and, if not integral, a primary part of the Thermal Protection System.
Inadequacy of the lack of a requirement for passenger accommodations
A stated purpose of this prize, as discussed in a prior posting, is to promote “commercial passenger travel”. Other than this one mention, the term “passenger” is nowhere else used in the draft enabling legislation.
The requirement to win the prize includes having at least a one metric ton payload capability, which includes two crew members. I would have expected, if the intent is to promote commercial passenger travel, that the payload requirement include accommodations for X number of passengers in addition to the two crew members. This would ensure that the appropriate passenger/crew accommodation, volume, life support, egress, etc., requirements for the passengers would be demonstrated as these may be expected to have a significant impact on the design and sizing of the flight system.
Let’s assume that each crew member and passenger, in their spacesuit, has a mass of 100 kg. Thus, the prize requirement of one metric ton should include the installed ability to transport two crew members and eight passengers with a total mass of one metric ton. This would be a suitable prize requirement supporting the development of a true commercial passenger transportation capability. However, without such an explicit requirement to accommodate two crew members and X number of passengers, the mass of equipment supporting the crew and passengers can be assigned to be a part of the one metric ton payload. Obviously, the number of passengers would then the small, perhaps zero, with a “winning” design having little commercial viability. The proper definition of what comprises the one metric ton payload should be made clear.
In the next posting, I’ll focus on proposed changes to the draft legislation to address the criticisms I’ve raised.