John Maynard Keynes

Keynes's central break with classical economics is that the level of output and employment is set by aggregate (effective) demand, not by the labor market clearing at full employment. An economy can settle, and persist, at an equilibrium below full capacity when desired investment falls short of full-employment saving. There is no automatic mechanism guaranteeing that private spending decisions sum to full employment (Keynes 1936; DOI 10.1007/978-3-319-70344-2). For space, the analogue is that there is no automatic mechanism guaranteeing private launch, R&D, and infrastructure spending will sum to the socially optimal level of space capability - the demand for new space capital can sit chronically below its social value.

An initial increment of autonomous spending (especially investment) raises income by a multiple of itself, the multiple being governed by the marginal propensity to consume / re-spend. The modern empirical literature confirms the multiplier is state-dependent: government-purchase multipliers are substantially larger in recession than in expansion (Auerbach & Gorodnichenko 2011; DOI 10.3386/w17447), and public *investment* in particular crowds *in* private investment for financially constrained firms rather than crowding it out (Espinoza, Gamboa-Arbelaez & Sy 2020; DOI 10.5089/9781513557694.001). This is the evidentiary backbone for treating anchor public space spending as a demand and capacity multiplier, not merely a transfer.

Investment proceeds to the point where the expected yield on a marginal unit of capital (its marginal efficiency) equals the rate of interest. Because the marginal efficiency depends on uncertain future returns, investment is volatile and interest-rate-sensitive (Keynes 1936). For space, long-lived, high-fixed-cost assets (constellations, lunar infrastructure, launch capacity) have marginal efficiencies dominated by deeply uncertain, long-horizon revenue - precisely the configuration in which Keynes predicts private under-investment relative to the social return.

Major investment decisions rest on long-term expectations about an unknowable future; they are driven not by calculable probabilities but by a "spontaneous urge to action," animal spirits, and conventionally held confidence that can shift abruptly (Keynes 1936). The formal modern restatement shows that under search/matching frictions, beliefs *select* the equilibrium, so confidence is causally load-bearing for the level of activity (Farmer 2009/2012; DOI 10.3386/w14846). For space ventures whose payoffs lie decades out, expectations and confidence - not discounted cash flow alone - govern whether capital is committed.

The interest rate is a monetary phenomenon set by the demand to hold wealth in liquid form against the supply of money. In a liquidity trap, monetary easing cannot lower the relevant rate further and fails to revive investment, leaving fiscal policy as the effective lever (Keynes 1936). The space analogue is a "capability trap": when expected returns are too uncertain and too distant, no amount of cheap capital alone elicits the socially desirable investment, and a direct public-investment / risk-bearing instrument is required.

Keynes concluded that a "somewhat comprehensive socialisation of investment" - not of ownership, but of the *aggregate volume and direction* of investment - would be needed to secure full employment, with the state bearing risk and setting direction where private incentives fall short (Keynes 1936). The modern operationalization is mission-oriented innovation policy, in which the state is a directional, risk-bearing investor that shapes and co-creates markets rather than merely fixing them (Mazzucato 2018; DOI 10.1093/icc/dty034). Apollo is the archetype; today's space programs are the live test case.

Keynes's argument is for *competent* public investment, not for spending as such. The honest reviewer must hold the symmetric critique: state direction of resources can fail through rent-seeking, capture, and poor information (Krueger 1990; DOI 10.1257/jep.4.3.9). Demonstrating a market failure is necessary but not sufficient to justify intervention; the candidate must also show the public instrument will not fail worse.