WASHINGTON--Dogged by rumors that Ares I rocket would not be able to lift the Orion Crew Exploration Vehicle if the booster was built as currently envisioned, NASA's Constellation program manager has shot back at unnamed critics in an e-mail missive he said he wrote to set the record straight.

"[M]any who carp from the sidelines do not seem to understand the systems engineering process. They instead want to sensationalize any issue to whatever end or preferred outcome they wish," wrote Jeff Hanley the NASA official leading the development of the rockets and spacecraft the United States is building to replace the space shuttle and to return to the Moon.

In the Nov. 13 e-mail, which circulated beyond NASA just within hours after he hit the send button, Hanley said he was writing in part to respond to a posting that had appeared over the weekend on the widely-read website NASA Watch declaring "Big Problems with the Stick."

NASA Watch's short Nov. 11 posting said the Ares I, also known as the Stick, "is underpowered to the tune of a metric ton or more" and would not be able to lift Orion. The information was attributed to reports from "sources inside the development of the Ares I launch vehicle."

What NASA Watch was reporting was the latest twist on what the aerospace community has been whispering about for months--that the space shuttle-derived design NASA picked for Ares I and its heavy-lift follow-on, the Ares V, is rife with problems and the agency would be better off taking some other approach.

That the aerospace community was buzzing with talk of Ares problems was not lost on Hanley and other senior NASA officials. Steve Cook, NASA's Ares program manager, was dispatched to speak at a Space Transportation Association breakfast here in October in an attempt to get ahead of the rumor mills, officials familiar with the behind-the-scenes preparations said.

Hanley said in an interview he normally does not respond so directly to what he characterized as misinformation that appears in "the pseudo media--blogs and so forth."

But the NASA Watch post spurred him to action. Hanley sent his e-mail, he said, to "a few dozen Constellation leaders throughout the program"--a long enough distribution list, it would seem, to ensure the message leaked to an even wider audience.

"I thought it was important that we set the record straight on some of the external stuff that's been going around. I don't want people to think that because they don't see us responding to it on a regular basis that has any basis in truth," said Hanley, who spoke to Space News in a Nov. 15 telephone interview from Johnson Space Center in Houston, where the agency's first systems requirement review for Orion and the Ares rocket had wrapped up the day before.

Hanley was joined on the interview by Cook and Scott Horowitz, NASA's associate administrator for exploration systems.

Hanley said the review, which was attended by NASA Administrator Mike Griffin and the agency's chief engineer, Chris Scolese, found that Ares I remains on track to lift the Orion spacecraft with performance to spare.

Reiterating points made in his e-mail, Hanley said the latest analysis shows that Ares I can lift (58,000 pounds) 26,100 kilograms to its low Earth orbit drop-off point. Its sole intended payload, Orion, is still running 15-20 percent below its NASA-imposed 48,500-pound (21,825-kilogram) weight limit fully fueled, he said.

The Ares I main stage is a larger five-segmented version of a space shuttle solid rocket booster. The rocket would be topped with a liquid-oxygen- and hydrogen-fueled upper stage powered by an updated version of the J-2 engine that flew on the Saturn 5.

NASA originally intended to use the shuttle's smaller four-segment booster for the Ares I main stage and use a more powerful shuttle main engine for the upper stage, but decided in January to go with a five-segment main stage and a J-2X for the upper stage in order to achieve greater commonality with the Ares V, the heavy-lift rocket NASA intends to start developing around the end of the decade for Moon missions.

The Ares V, as envisioned, will use a pair of five-segment solid rocket boosters to help lift a cryogenic main stage powered by a cluster of the RS-68 engines now used on the Delta 4 rocket. The J-2X would come back in play as the main engine for the Ares V's Earth Departure Stage.

Cook, who runs the Ares program from Marshall Space Flight Center in Huntsville, Ala., said the mass and performance of Ares I and its Orion payload do get a lot of attention from the program, but he said claims that Ares I is underpowered are simply not true.

"Mass and performance are things you are going to always have to track on any aerospace vehicle, especially one that wants to go to orbit," Cook said. "You've got to treat it seriously and you have got to keep up with it as you go along. But we can lift what we need to lift with 15 percent performance margin."

Cook said Ares I weight and performance projections have fluctuated in the 10 months since NASA switched to the five-segment/J-2X combo, but said that is typical for any aerospace vehicle making the transition from detailed concept to preliminary design.

"We've started building the vehicle from the bottom up," Cook said. "And the first time you do that, you find that everybody starts putting margin in the system and it comes out weighing more and getting less performance than you initially projected," he said. "Then you start working back down, 'why is it that way?' and you work it back down through the process. This is standard 101 stuff that goes on. It's fluctuated up and down. It's part of the normal design cycle."

Citing an example, Cook said the Ares I weight estimates shot up earlier this year when the program looked for ways to reduce manufacturing costs on the upper stage by penciling in "all kinds of commonality", such wall thickness and common domes.

"Well, it turned out it wasn't going to work so we had to back off and be less aggressive in how did the design and do it more like we had done upper stages in the past," he said.

Cook said the Ares I upper stage is very similar to the Saturn-5's third stage in size and performance. "It held 240,000 pounds of liquid oxygen and liquid hydrogen. We hold [280,000 pounds]. It had one J-2 engine. We have one J-2X engine. So we are a little bit bigger and a little bit higher thrust, but we are in that same thrust category," he said. "That gives us confidence that what we are shooting for will work."

The preliminary design review for Ares I is in February 2008, about 14 months away. The critical design review, when NASA nails down the design and starts producing the vehicle, is slated for late 2009.

Orion's preliminary and critical design reviews are slated for summer 2008 and summer 2009, respectively.

Hanley said Denver-based Lockheed Martin Space Systems, selected in late August as the Orion prime contractor, has spent the last two months incorporating a few NASA changes into its winning spacecraft design.

A revised reference design for Orion, Hanley said, is not due until early December. Still, he said, all indications are that Orion is staying well within its mass targets.

"If you held their feet to the fire and asked them what is their no-kidding projected mass, it would be something on the order of 15-20 percent lower than 48,500 pounds (21,825 kilograms)," he said. "They have plenty of margin."

Hanley said weight will remain at the top of his watch list until Orion and Ares actually launch. Weight estimates will fluctuate, he said, as engineers work the trades offs that go along with designing a spacecraft or rocket.

"Six months from now, the Orion guys could come in and say, 'hey, we are 1,000 pounds (450 kilograms) over.' Okay, so back to work. Go solve it," Hanley said. "That's the way the game is played."

Ares gossip heard from industry sources is often accompanied by subtle, and sometimes not so subtle, advocacy for alternative approaches, such as using the Atlas 5 or Delta 4 Evolved Expendable Launch Vehicles as the basis of NASA's new transportation system.

Cook said that is to be expected given the stakes.

"Part of this is because we haven't done a design of an exploration-class system, whether it's the crew vehicle or the launch vehicle, in 40 years ... so when it happens, everybody is clamoring to get a piece of it and want to help" Cook said. "And I don't think it helps, frankly, that over the last 15 years NASA has been a little inconsistent in what it wants to do. But when the president put out the vision in 2004 we got a very clear message of how to go be focused. And that was the first focusing event in well over a decade."

Horowitz dismissed anonymous claims of trouble on Ares as "rumblings from people who didn't get their particular favorite rocket design picked."

Horowitz has championed the single stick design for Ares I since shortly after the 2003 Space Shuttle Columbia accident claimed the lives of seven of his fellow astronauts. He continued his advocacy for what some called "the Scotty rocket" during a brief stint at ATK Thiokol, the Promontory, Utah-based solid-rocket booster firm picked to build the Ares I main stage.

Horowitz said NASA looked at 10,000 to 20,000 iterations of different designs as part of an intensive Exploration Systems Architecture Study before selecting the crew and cargo launcher concepts the agency unveiled in September 2005.

"Are there other solutions that would work? Sure," Horowitz said. "But so does this one. This is ours. And this is where we are going. And occasionally you're just going to get noise in the system. We try to educate people. It's just noise."