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<!DOCTYPE HTML>
<HTML>
<HEAD>
<title>Chariots For Apollo, ch6-4</title>
<meta http-equiv=Content-Type content="text/html; charset=UTF-8">
</head>
<BODY BGCOLOR="#FFFFFF">
<p>
<h2>Hatches and Landing Gear</h2>
<p>
The lander originally had two docking hatches, one at the top center of
the cabin and another in the forward position, or nose, of the vehicle,
with a tunnel in each location to permit astronauts to crawl from one
pressurized vehicle to the other. (Extravehicular transfer between craft
remained an emergency backup method.) After injection into a translunar
trajectory, a course toward the moon, the command module pilot would
turn his ship around, fly up to and dock with the lander's upper hatch,
and then back the two vehicles away from the spent S-IVB third stage.
This top-to-top docking arrangement aligned the thrust vector of the
service module propulsion engine with the centers of gravity of the two
spacecraft, thus avoiding adverse torques or tendencies to tumble during
firings for midcourse corrections and injection into lunar orbit. The
crew would enter the lunar module through this hatch. When the lander
returned from the moon, however, the front hatch would be used for
docking and crew transfer. With no windows in the top of the lander, the
lunar pilots would be flying blind if they docked with the upper hatch.
One of Grumman's human factor experts later said, in an apt analogy,
"It's nice to see the garage . . . when you drive into it."<a
href = "#source15"><b>15</b></a>
<p align=center>
<img src = "images/c153c.jpg" ALT="Improved LM features">
<p>
<cite>The drawing shows improved lunar module features - ladder, porch,
hatch, and rendezvous window (above the triangular window).</cite>
<p>
<hr>
<p>
By spring 1964, NASA and Grumman engineers were thinking of deleting the
front docking procedure and adding a small window above the lunar module
commander's head. This overhead window might add seven kilograms weight
and some extra thermal burden, but cabin redesign would be minimal. The
added weight would be offset by eliminating the front tunnel and the
extra structural strength needed to withstand impact loads in two areas.
Eliminating forward docking had another advantage. The hatches could now
be designed for a single purpose - access to the command module through
one hatch and to the lunar surface through the other - which certainly
simplified the design of the forward hatch. NASA directed Grumman to
remove the forward docking interface but to leave the hatch for the
astronauts to use as a door while on the moon.<a href =
"#source16"><b>16</b></a><p>
Once the location of the hatches was settled, getting the astronauts out
and onto the lunar surface had to be investigated. Using a cable
contraption called a "Peter Pan rig" to simulate the moon's
gravity, Grumman technicians looked into ways for the crews to lower
themselves to the lunar surface and to climb back into the spacecraft.
When astronaut Edward White, among others, scrambled around a mockup of
the lander, using a block and tackle arrangement and a simple knotted
rope, he found that both were impractical. In mid-1964 a porch, or
ledge, was installed outside the hatch and a ladder and handrail on the
forward landing gear leg. When the astronauts discovered they had
trouble squeezing through the round hatch in their pressurized suits and
wearing the bulky backpads, the hatch was squared off to permit easier
passage.<a href = "#source17"><b>17</b></a>
<p align=center>
<img src = "images/c153a.jpg" width=400 height=509 ALT="Knotted rope on LM">
<p>
<cite>Astronauts found a knotted rope from the lunar module difficult to
climb down (or up)</cite>
<p>
<hr>
<p align=center>
<img src = "images/c153b.jpg" width=410 height=535 ALT="Ladder on LM leg">
<p>
<cite>The addition of a ladder on a landing gear leg made the task much
easier.</cite>
<p>
<hr>
<p>
All these design features, although unusual, appeared to be compatible
with the lunar environment - at least the engineers did not entertain
any special worries. But the landing gear was different. The design of
the legs and foot pads depended on assumptions about the nature and
characteristics of the lunar surface. In the absence of any firm
knowledge and with scientific authorities differing radically in their
theories, how should one design legs to support a craft landing on the
moon?<p>
Grumman had first considered five legs but, during 1963, decided on
four. The change was dictated by the weight-versus-strength tradeoff
that had produced the cruciform descent stage, with its four obvious
attachment points. The revised gear pattern also greatly simplified the
structural mounting of the vehicle within the adapter. Four legs set on
the orthogonal axes of the lander (forward, aft, left, and right) mated
ideally with the pattern of four reaction control "quads" (the
basic four-engine package). The quads were rotated 45 degrees so the
downward-thrusting attitude control engine fired between the two nearest
gear legs, overcoming a severe thermal problem of the five-leg
arrangement.<a href = "#source18"><b>18</b></a><p>
While Bethpage was wrestling with the legs, Houston decided it had been
too optimistic about the load-bearing strength of the lunar surface in
the request for proposals. The resulting revision placed heavier demands
on the landing gear, and Grumman had to enlarge the foot pads from 22 to
91 centimeters in diameter. The bigger feet made the gear too large to
fit into the adapter. A retractable gear therefore replaced the simpler
fixed-leg gear. Retractability also figured in the shift from five to
four legs - the fewer to fold, the better.
<p align=center>
<img src = "images/c153d.jpg" width=485 height=404 ALT="LM in adapter">
<p>
<cite>The fit of the LM inside the adapter during launch.</cite>
<p>
<hr>
<p>
Leg experts at Grumman had to change the geometry of the undercarriage,
devise the best structure for impact absorption and stability upon
landing, and choose the most suitable folding linkages. A broad program
of computer-assisted analysis at Houston and Bethpage was used to
determine the worst combinations of conditions at impact. The studies
were reinforced by drop tests of lander models at Houston, Bethpage, and
Langley. There were also plans to drop-test full-sized test articles to
check out the new designs.<a href = "#source19"><b>19</b></a><p>
During 1963 Grumman engineers continued to worry about the nature of the
lunar surface and to carry on theoretical and simulation studies of
lunar geology and soil mechanics, with the support of such consulting
firms as the Stevens Institute of Technology in New York and the Arthur
D. Little Company in Massachusetts. Much of this work covered the
interaction between vehicle and surface at the moment of landing. What
would happen to the landing gear at touchdown? Would the lunar dust that
might be kicked up by the descent engine exhaust obscure the landing
site? Would soil erosion affect the stability of the lander? Washington
also assisted in this research. In mid-1963, Bellcomm surveyed all that
was being done inside and outside NASA and suggested that a backup gear
be developed, in case the surface should be more inhospitable than it
appeared.<a href = "#source20"><b>20</b></a><p>
But Grumman could not wait on the outcome of these studies. At meetings
in Houston in October and November, contractor engineers described gears
that tucked sideways (lateral folding) for stowage in the adapter; a
tripod arrangement (radial), with three struts meeting at the base just
above the footpad, that tucked inward; and a cantilevered device, with
secondary struts for extra strength that folded inward against the
vehicle for stowage and braced the leg when deployed for landing.
Houston and Bethpage selected the cantilevered version. Somewhat
narrower than the radial one, it was, in many ways, more stable. It had
other advantages: less weight, shorter length for easier stowage, and a
simpler, and therefore more reliable, folding mechanism.<p>
A landing gear for the lunar surface had to be designed for varying
landing conditions, such as protuberances, depressions, small craters,
slopes, and soil-bearing strength. To achieve the necessary stability,
the landing gear had to be able to absorb a diversity of impact loads.
Houston and Bethpage met this challenge by using crushable honeycomb
material in the struts, so the gear would compress on impact. A
principal advantage of honeycomb shock absorbers was their simplicity.
Since they had to work only once, the more common hydraulic shock
absorbers and their complexities could be avoided. Subsequently,
crushable honeycomb was also applied to the large saucerlike foot pads
to improve stability further for landing.<a href =
"#source21"><b>21</b></a>
<p>
<hr>
<p>
<a name = "source15"><b>15</b>.</a> Donald K. Slayton to ASPO, Attn.:
William A. Lee, "Docking Operational Requirements," 2 Dec.
1963; Kelly, "Technical Development Status," p. 29; "Some
Notes on Evolution of LEM," pp. 1-2; Sherman interview.<p>
<a name = "source16"><b>16</b>.</a> Joseph P. Loftus to Chief, Sys. Eng.
Div. (SED), "Disposition of TM-1 mockup review chit no.
A9-4," 28 April 1964; Slayton to ASPO, Attn.: Maynard, "LEM
overhead window experiment," 6 May 1964; LEM PO,
"Accomplishments," 14–20 May 1964.<p>
<a name = "source17"><b>17</b>.</a> Sherman interview; Kelly,
"Technical Development Status," p. 29; "Some Notes on
Evolution of LEM," pp. 3-4.<p>
<a name = "source18"><b>18</b>.</a> Kelly, "Technical Development
Status," p. 48; John L. Sloop to Dep Admin., NASA, "Comparison
of technology readiness at start of Apollo and Shuttle," 11 Feb.
1972, with encs.; Maynard, interview, Houston, 18 Feb. 1970; Grumman
Report no. 1, LPR-10-1, 10 March 1963, p. 5, and no. 3, LPR-10-6, 10 May
1963, p. 7.<p>
<a name = "source19"><b>19</b>.</a> Grumman Report no. 4, LPR-10-7, 10
June 1963, p. 13; Robert A. Newlander to John W. Small and Walter J.
Gaylor, "LEM Landing Gear," 8 May 1963; Newlander to Mgr.,
RASPO, "Trip . . . to MSC on May 20, 21, 22, 1963 to attend
Mechanical Systems Meeting," 27 May 1963; MSC Director's briefing
notes for 25 June 1963 MSFMC meeting; Decker draft memo to Grumman,
"Landing Gear," 21 Aug. 1963; ASPO Weekly Activity Report,
5–11 Sept. 1963, pp. 7-8; Newlander to Gaylor, "1/6 Scale Model
Tests," 19 Sept. 1963; Axel T. Mattson to MSC, Attn.: Shea,
"Langley Research Center Tests of Interest to Project Apollo,"
7 Aug. and 17 Nov. 1964; Maynard memo, "Notice of LEM Structures
and Landing Gear meeting," 15 Dec. 1964; Kelly memo,
"Re-definition of TM-5 Test Program," 15 Dec. 1964, with enc.,
R. A. Hildermen to Rathke, Kelly, and Whitaker, "Elimination of
Lift Systems for TM-5 and LTA-3, Drop Testing and Configuration of
TM-5," 10 Dec. 1964.<p>
<a name = "source20"><b>20</b>.</a> Gavin, interview, Bethpage, 11 Feb.
1970; Ferdman to Eugene M. Shoemaker, 24 May 1963; Maynard to ASPO Prog.
Cont., Attn.: James A. York, "GAEC Letter LLR-150-550, 'Landing
Performance in a Lunar Dust Environment,' dated 29 October 1964,"
21 Dec. 1964, with enc., John C. Snedeker to MSC, Attn.: Neal,
"System Engineering Study . . . Request for Approval. . . ,"
29 Oct. 1964; Thomas L. Powers, "Lunar Landing Dynamics," 17
June 1963; Hugh M. Scott memo, "Minutes of meeting on the LEM
landing gear held at MSC on September 3, 1964," 15 Sept. 1964,
with encs.; Bendix, "Final Report: Lunar Landing Dynamics Specific
Systems Engineering Studies," MM-65-4 (Bellcomm Contract 10002),
June 1965; Robert E. Lewis to Asst. Chief, SED, "OMSF specified LEM
tilt angle on lunar surface, constraints imposed by G&C Performance
Requirements," 20 May 1964; General Electric, "Study of the
Postlanding Tilt Angle of the LEM," TIR 545-S64-03-006, 21 May
1964; William Lee to Chief, SED, "LEM postlanding tilt angle,"
2 June 1964; Maynard to LEM PO, "Exhibit E to LEM Statement of Work
- Change to incorporate LEM lunar postlanding attitude," 11 June
1964; Decker to Grumman, Attn.: Mullaney, "Landing Gear Design
Development," 4 June 1964.<p>
<a name = "source21"><b>21</b>.</a> ASPO Status Reports for period
ending 16 Oct. and for week ending 19 Nov. 1963; Grumman Report no. 10,
pp. 2, 10, and no. 23, LPR-10-39, 10 Jan. 1965, pp. 1, 15; Rector memo
to LEM Proc. Off., "Change from a 180″ [457-cm] Tripod Landing
Gear to a 160″ [406-cm] Cantilever Design," 13 April 1964;
Robert E. Vale and Scott, telephone interviews, 20 March 1975; Rector to
Grumman, Attn.: Mullaney, "Landing gear design criteria," 11
Dec. 1964; abstract of LEM Structures and Landing Gear Systems Meeting,
21–22 Dec. 1964, with encs.; Bendix Products Aerospace Div., "Space
Vehicle Landing Gear Systems," brochure, November 1963; Raymond J.
Black, "Quadripedal Landing Gear Systems for Spacecraft,"
reprinted from <cite>Journal for Spacecraft and Rockets</cite> 1, no. 2
(March–April 1964): 196-203; MSC news release 64-9, 15 Jan. 1964;
William F. Rogers, "Lunar Module Landing Gear Subsystem," AER
TN S-316 (MSC-04797), review copy, January 1972.
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